« ПретходнаНастави »
reports are made must be regarded as having only a tentative value. Other lines of experimental zoology are attracting much attention, and the newer science of oecology, has, in the United States, received some impetus from workers at the University of Chicago. The European War cut off a large number of periodicals, and undoubtedly many researches were for that reason not brought to the attention of zoologists. In the following paragraphs important announcements of advances in general zoology will be taken up first, and followed by some more general reports.
Protozoa. Woodruff and Baitsell decided that protozoa may be kept for an indefinite period without conjugation if a proper environment is furnished. (See below.) Lund, working on Bursaria, and Metalnikov, on Parametrium, decided that the animals are able to discriminate between nutritious, on the one hand, and nonnutritious or toxic, materials on the other. Bursaria will throw off vacuoles containing indigestible substances, while retaining those with digestible materials, and Paramcecium after having once taken toxic or nonnutritious substances, will not take in these same substances, though it will take in others. Metalnikov considers this a true process of learning.
Porifera. Parker found that a "finger" of a Bermuda sponge 10 cm. long and 4 cm. in diameter, would discharge about 78 liters of water in a day. He did not attempt to determine the character of the organisms brought into the animal by this current. The highest pressure obtained in any current flowing through the oscula of these sponges was 2.5 m.m.
Annelids. Baylis described a new genus and species of Oligoehffita (Aspidodrilus kelsalli) living on the surface of an undescribed earthworm. He concluded that it was probably commensal rather than parasitic, since its alimentary canal contained vegetable dgbris. Korscheldt reported on the length of life of earthworms. The longest life recorded among his specimens was a Helodrilua longua which lived for over 10 years. Lumbricus terrestris lived six years, and Eiaenia fcetida about four and one-half years. It should be noted that these are observations on animals in confinement, and their life is possibly longer than in their natural environment, where enemies abound. Korscheldt observed that, on the approach of cold weather, these earthworms burrow to below frost level, and roll up in a ball at the bottom of their tube, passing into a regular hibernating condition.
Mollusca. Kuhn, working on the biology of the snail, Helix pomatia, found that the animal may enter into the hibernating condition at any time of the year; in the winter as a reaction to temperature (though here also a seasonal rhythm can be shown), at other seasons as a protection against drying. The animal draws into the shell and secretes an operculum over the opening, but the chalk deposit in this operculum appears only at the approach of winter. If the operculum is in good condition, the animals will resist very unfavorable conditions, and those who die do so because of some defect in the operculum. Experiments showed that respiration takes place through both the operculum and the shell. A decrease in the water content of the liver and muscles, and a deposit
of lecithin in the liver, and of glucose in the liver, foot muscle, and albumen gland, marks the progress of the hibernation. Moisture is of the utmost importance to the animal, for it moves only in a moist atmosphere and reacts to food only if the latter be damp. According to Flossner, the difference between a simple diaphragm and the heavy operculum of the winter hibernation of the snail is merely that the latter has more calcium carbonate Thus operculum formation is largely a matter of crystallization of calcium carbonate.
Orton had earlier found that the food of Crepidula is similar to that of the oyster, and the question arose as to the function of the radula. He later found that the fine particles of the food are drawn in by the gill currents, combined with mucus and passed forward to the head. The radula bites off bits of this mags, and passes them into the mouth. Further study led him to the conclusion that the gills of lamellibranchs have essentially this same function to collect and combine food with mucus, and that they are only partly for respiration, this latter function being restricted to what he called the branchial extensions of the gills.
Among the collections of the Michael Sars Expedition were a number of cephalopods, on which reports were made during 1014. Of interest was the collection of several early stages of Spirula, taken in the plankton near the Canary Islands. The youngest stages were 6 to 9 m.m. long, and a number of older specimens were found. A new cephalopod, Cirrothauma murrayi, was remarkable for the gelatinous semitransparent character of the body.
Arthropoda. D. C. Worcester described a flying crustacean 15 to 26 cm. long, which occurs off the coast of Palawan in the Philippine Islands. The animal can rise above the surface of the water and fly in the same manner as the flying fish.
The largest lobster on record was sent to the American Museum of Natural History in September of 1913. It was 38 inches long, and weighed 21 pounds.
While the beaver parasite Platypsylla cantoris is the classic example of a parasitic beetle, Kellogg described other cases where this habit seems to be forming. Leptunus testaceus occurs in both Europe and America in nests of field mice and shrews, and shows beginnings of characteristic changes due to a parasitic life. Lyrosoma opacum is found on isolated rocks in the North Pacific, and is apparently carried from rock to rock by birds. This seemed to Kellogg to be but a step from true parasitism, as the change from feeding on feathers in the nest to feeding on the bodies of the living birds would be very easy to take.
Mclndoo studied the olfactory reactions of the honey bees and concluded that the olfactory organs are pores found on the bases of the wings and on the legB, the antennae having no function in this connection. In the bee, he found a scent producing organ situated between the fifth and sixth abdominal somites. This secretes a volatile substance which is held in and evaporates very slowly when the abdomen is straight, but evaporates and thus diffuses rapidly through the air when it is flexed.
Vertebrates. While there is still disagreement as to the mechanism of the flight of fishes,
Ridewood claimed to have discovered that a South American fresh water flying fish, Qastropiteous, flaps its fins when it "flies," while the ordinary flying fish, Exocetus, merely glides. Mayhoff studied the mechanism of the migration of the eyes in flatfish, and decided that muscular action is not involved, but that migration is due to the cooperation of several factors, chiefly movements of the head skeleton.
Laurens stated that frog tadpoles show no response to light but that Amblystoma larvte are positively phototactic even if deprived of eyes. In the latter case, he thought that nerve endings in the skin were able to receive light stimulations. Somewhat similar results were obtained by Ackert, who studied the nerve endings in the skin of the bat, and, from their distribution and the review of the literature,. concluded that a blinded bat is able to discover when it is approaching an object, by the effect of the condensation of the air against the skin, thus stimulating the nerve endings. In the amphibian Necturus, Eyclesheimer found that the reactions to light were essentially the same if the head were cut off as in the intact animal. This is due to a "dermatopteric" sense.
Marie Phisalix concludes from a study of the poison apparatus of snakes, that these are a direct development of the use formerly made of these organs in digestion. They originally were simply paralyzing organs and facilitated swallowing by keeping the prey quiet. Their poisonous character is simply an exaggeration of their primitive function.
Sex. While the question of the meaning of sex is still entirely unsolved, zoologists in general believe that light may be thrown on it by a study of the conjugation processes in the Protozoa. Paramceoium is the form most frequently studied, and here conjugation is essentially a transfer of nuclear matter from each one of, a pair of individuals to the other. This was interpreted to mean that this transfer is in some fashion a process of rejuvenation, each giving to the other something which it lacks but which is essential for its continued existence. Weismann, on the other hand, argued that it is not a rejuvenation process, but a method of producing variability in the race by varying its nuclear composition. Later workers reached conflicting results (consult New International Year Book for 1913), a condition which Calkins decided was due to the fact that different workers used different races, his conclusion being that in Paramceoium there is a definite life cycle, and that death will sooner or later occur unless conjugation takes place.
Woodruff, on the other hand, has been able to keep Paramceoium for more than 4500 generations without any conjugation, though individuals taken from these cultures and given an opportunity to conjugate will do so, thus showing that they are not without the ability. During this time there appeared marked periodic variations in the division rate, and Woodruff and Erdmann published, at some length, the results of a study of the nuclear changes accompanying the rhythms. From October, 1913, to April, 1914, specimens were taken daily, stained, and mounted to show the nuclear conditions. In general, nuclear changes occurred which were very similar to those which accompany normal conjugation. The macronucleus breaks up and eventually disappears, as it does during conjuga
tion, though there are some morphological differences between the two cases. The micronuclei divide as in conjugation, though possibly the last division leading to the "migratory" nucleus does not take place. After the macronucleus disappears, either the cell divides, or a reorganization takes place without this division. In either case the new nuclear equipment comes from a division of the micronuelear matter left in the cell. The authors' conclusion was that the Paramceoium, if not allowed to conjugate, periodically reorganizes itself by a process which is similar to conjugation, but without any transfer of nuclear matter. This they called "endomixis." This endomixis fills the same place in the life of the animal that conjugation does, and is sufficient to prevent senile degeneration. This might be called a process of parthenogenesis, but the authors thought that the nuclear conditions were different from those of true parthenogenesis.
These results were discussed by Hertwig, who compared them with results which he obtained on this same species 25 years earlier. These had been obtained only in Paramceoium aurelia, which has two micronuclei, and those with only one micronucleus, so far as has been discovered, do not show them. Hertwig suggested that there was possibly a fertilization of one micronucleus by another, thus a true process of autogamy. Hertwig*s general conclusion was that these experiments do not demonstrate that protozoa are "potentially immortal," but instead indicate that the body of each, like the body of the metazoa, contains in itself a mechanism of reorganization; while a part of the body dies, a portion of it is rebuilt into a new individual.
In the rotifer Hydatina senta, Whitney claimed that he had been able to control sex by varying the food of the animals. A strain was used in which the percentage of males was very low, and this continued so long as the animals were fed on a flagellate, Polytoma. When a sudden change was made to another protozoon, Dunaliella, the grandchildren of those first treated showed a marked percentage of males, hence the conclusion that the food had determined the sex. Cases have been described where a change of temperature was followed by similar results. Whitney thought that these were really due to changes of the diet, for the rotifers were fed on mixed cultures of protozoa, and the variations in temperature by favoring one form rather than another, resulted really in a change of food. Hence it was the food rather than the temperature which was the active agent.
Geoffrey Smith, who for some years has been attempting an analysis of sex by observations on the crabs infested by Sacculvna, where a deterioration of sex organs follows parasitism, has, in collaboration with Hamm, continued this study on Btylops, a parasitic insect infesting the bee. Here they found that the ovary will disappear as a result of parasitism, but no loss of external sex characters follows this degeneration. In the male, no effects were noticed.
In the New International Year Book for 1913, mention was made of experiments conducted by F. R. Lillie, who found in an annelid, Nereis, and a sea urchin, Arbacia, a substance secreted by the egg which first acts as an agglutinator of the spermatozoa and subsequently
activates it so as to produce fertilization. Lillie, in 1914, continued his work on this substance in the egg of Arbacia. The mechanism by which this substance (to which he now gives the name "fertilizin") operates, can best be described by using the terminology of immunology, though Lilhe insisted that this terminology is employed only for convenience, and the analogy must not be pushed too far. Bearing this caution in mind, we may then regard fertilizin as a receptor, with a spermophile and an ovophilo combining group. When its spermophile group combines with the spermatozoon, the ovophile group is activated and by combining with the egg, causes fertilization. The egg is thus fundamentally self-fertilizing, a conclusion which has important bearing on the "amazing number" of agents that initiate artificial parthenogenesis. Contact of the spermatozoon with the egg is necessary in order that this process should start, and as soon as this occurs, another substance, "anti fertilizin," neutralizes the fertilizin, thus preventing the entrance of a second spermatozoon. Lillie compared this with the lysin theory of Locb, and concluded that the evidence is in favor of the belief that the egg rather than the spermatozoon contains the fertilizing substance.
Loeb, in rejoinder to this theory of Lillie's, described results obtained from a study of a California sea urchin, Strongylocentrotus purpuratus. Here he found also a substance which causes clumping of the spermatozoa which he thought identical with that described by Lillie, but which was not, in his opinion, a true agglutinator, for it does not work on spermatozoa deprived of their motility, while true agglutination would occur irrespective of any activity of the spermatozoa. He regarded the clumping as possibly a trophic reaction. Loeb also pointed out that if this is essential for fertilization, it ought to appear whenever true fertilization occurs. As a matter of fact, it appears only when eggs and sperm of the same species are mixed, and does not appear in cases of hybridization, even though there may be perfect fertilization.
Mutation. Jeffrey corroborated Davis (consult New International Yeab Book for 1912) in claiming that the so called mutations of Oenothera are hybrids breaking up into their component species. De Vries replied to this by saying that the mutation theory is not dependent on Oenothera alone, but is based on results of other experiments. As far as (Enothera is concerned, he claimed that the variability is greater than could be explained on any assumption of its hybrid condition.
Evolution. Decidedly revolutionary theories were proposed by Bateson in addresses prepared for delivery as President of the British Association for the Advancement of Science. Basing his belief on the results of his own experiments on plants, where he found that the appearance of a supposedly new character is always due to the removal of a previously inhibitory factor, Bateson stated his belief that what are apparently new characters in evolution, are always previously existing ones which have earlier been masked and not allowed expression. The only causes of variation are removal of an inhibitor; loss of a factor; quantitative change in a factor; and crossing. Therefore we have no reason to think of evolution as a progression from
simple to complex, but the reverse. Bateson says: "I have confidence that the artistic gifts of mankind will prove to be due not to something added to the makeup of an ordinary man, but to the absence of factors which, in the normal person, inhibit the development of these gifts." So far as is known to the reviewer, criticism of Bateson's position has been universally adverse.
Heredity. The late Professor Whitman of the University of Chicago, left, at his death, a large collection of pigeons on which experiments on heredity had been conducted for some years. These birds have been taken to the Station for Experimental Evolution at Cold Spring Harbor, where Professor Whitman's work is being continued by Dr. Riddle, under the auspices of the Carnegie Institution of Washington. In Germany, the first establishment of its kind in the country, an Institut fUr VererbungBiorschung was announced for the summer session of the Royal Agricultural High School in Berlin.
At the Maine Agricultural Experiment Station, Pearl and his colleagues continued work on genetics chiefly on problems connected with the domestic fowl. Much of Pearl's publications dealt with very technical phases of genetics, but in the annual report of the Station for 1914, he summarizes in simple form the most important of these results for the use of poultry breeders.
Morgan and his students continued investigations on the fruit fly (consult New InternaTional Year Book for 1913), with the results that further factors, especially of the "sex linked" kind, were isolated. Morgan also finds in the fruit fly a number of "lethal factors" which act so as to produce the death of the individual possessing them.
Morgan summarized the most important recent work on heredity, together with his conclusions on the question of chromosomes and sex determination, in a book, Heredity and Sex, which appeared at the end of 1913.
Since Morgan's flies had all been etherized, the suspicion might arise that the mutations reported in his experiments were in direct response to the ether stimulus and therefore not normal mutants. Experiments devised to test the probability of this kind of stimulus resulting in mutation, gave no reason to suppose that it had taken place.
Castle's earlier work had seemed to show that in breeding rabbits, the ear length of the offspring was a blend of that of the parents, thus seeming to be in opposition to strict Mendelian laws. East explained this result by the assumption of "multiple factors" for ear length, the latter varying with the number of factors that are present. MacDougall claimed that if multiple factors are present, back crossing ought to give greater variations than appeared before. The results of his experiments on rabbits seemed to show a greater variability under these conditions, and thus to confirm his theory.
According to the "pure line" hypothesis of Johanssen, selection can act only so as to isolate races already in existence, and can never produce anything new. East and Hays in tobacco, and Ewing in the inheritance of antenna! length of plant lice, found confirmations of this view, while Castle, on the other hand, reported evidence that selection did result in a definite increase or decrease beyond anything previously
present. Apparently the pure line question is as yet unsettled.
A commonly accepted belief among animal breeders, though largely abandoned by horse, cattle, and swine breeders, is the idea that if a female is first mated with a low bred male, her later offspring will be affected by the union, even though pure blood males may be employed for the later union. This is known as "telegony," and is not generally accepted by students of heredity, experiments made some years ago on breeding horses and zebras resulting in negative evidence. The subject was discussed again by Rabaud, who went over all the available evidence, and concluded that there is nothing to be said in its favor. There might possibly be some interchange of material between the blood of the foetus and that of the mother, so that after one impregation she would be different from what she was before, but this would be too indefinite to be of any importance in a discussion of heredity.
Newman studied the mode of inheritance in various teleost hybrids, and concluded that while the spermatozoon initiates the development, it takes no active part in the formation of the embryo until, at least, the beginning of gastrulation. At this time it begins to play a part in the formation of the embryo, and if it fails to cooperate with the egg components, the embryo does not develop normally. He was unable to get any decisive results bearing on the question of Mendelian inheritance in these hybrids.
Jordan discussed the available data on lefthandedness in man, and concluded that this acts as a Mendelian recessive, though occasionally modifications of this rule appear.
Chromosomes. The possible role of the chromosomes as carriers of hereditary qualities, continued as a subject for discussion during the year, and probably the majority of workers took the position both that the chromosomes are carriers of hereditary qualities, and that the accessory chromosome in some way determines sex. Muller, for example, thought that the discovery of a new, bent-winged, mutant in the fruit fly gave him data for a final analysis of the function of the separate chromosomes in this animal. There are first a pair of sex chromosomes, X and Y, and with the former are linked over 30 genes, the Y apparently having no function. Two pairs of "autosomes" (chromosomes other than sex chromosomes) are correlated with two other groups of genes with about 20 in each group, and a pair of smaller autosomes whose function has been in doubt, but Muller thinks they are associated with the newly discovered wing mutation. Since the chromosomes of this third group are small, the genes are closer together and of smaller size, and thus they do not mutate so often as in the larger chromosomes.
VVodsadelek reported the discovery of an accessory chromosome in the horse, though he had no information as to its relation to sex determination. Jordan reported that this accessory occurs in some mammals and hot in others, and that no definite relation exists between the classification of these forms, and the presence or absence of the chromosome. The theory that this determines sex can hold in mammals only if we assume that the accessory occurs in the female in some species and the male in others.
A study of the ovogenesis would be necessary in order to determine this point. Guyer thought that an X or accessory chromosome is found in the male of the Black Langshan breed of fowl, thus making the fowl heterozygous for sex. The results of breeding of this fowl, however, indicate that the female is thus heterozygous, and Pearl and Boring reinvestigated the spermatogenesis of the animal with the result that they were unable to find any indication of the accessory chromosome, though there were many chromosomes which might be thus interpreted. Their decision was, therefore, that Guyer's interpretation was incorrect. Metz showed that the comparative chromosomal condition in several species of the fruit fly might indicate a definite progress, but he was unable to correlate this with any constant gradation of structures among bodily characters. Doncas reviewed the relation of chromosomes to inheritance of Mendelian characters, and concluded that the arguments connecting chromosomes with Mendelian segregation are strong, but not indisputable. The arguments connecting chromosomes with sex are stronger. He considered that sex is not determined by the presence or absence of a sex factor, but by a type of metabolism induced by the presence or absence of certain chromosomes.
On the other hand, Foot and Strobell, reporting on the heredity of the intromittent organ in insects, decide that something outside the chromosome is responsible for the transmission of the characters in the observed fashion.
Boveri suggested that malignant tumors are due to the aberrant action of the chromosomes in the cells, experiments on echinoderm eggs indicating that abnormal chromosomes are followed by abnormalities in the body.
Protective Coloration. J. C. F. Fryer studied the polmorphism of Papilio polytes by pedigree breeding, and while he came to no very clean cut conclusions, he was inclined to the belief that the mimicry displayed by the female is of very little use to the animal in its native habitat of Ceylon. Abbott studied the question of mimicry in the genus Limenitis by statistical methods. Limenitis arokippus is a mimic of Anosia plexippus, and Poulton supposed that when Limenitis arthemis occurred in the Bame locality with Anosia plexippus, there would bo variants of the former in the direction of resemblance to the latter, and thus toward the formation of the Limenitis archippus. A statistical study of a number of the color markings of the insect gave no evidence that any such change as was postulated was taking place.
Germ Cycle. Weismann's theory of heredity was largely based on the idea that a germ plasm is continuous from one generation to the next, and that this material in the egg is more or less isolated from body-forming material, and follows a definite path to the sex organs of the new individual. The subject has again been studied by Hegner, who gave a general review of the literature on Crustacea and Insects where this "Keimbahn" has been studied. In the egg of the insect Copidosoma, the entire chromosome content of an oocyte nucleus forms the "Keimbahn" determinant, while another oocyte fuses with this and forms the nucleus of the developing egg. Thus every fully formed egg of Copidosoma consists of two oocytes which have fused. Hegner has summarized the work that