paralyzed or in a state of partial rigor. Then often there is a period of attempted crawling in which the caterpillar moves forward little if at all, perhaps with spasmodic spinning movements; finally a series of feeble but regular muscular contractions may be observed, going from rear to front, like an echo of the usual crawling movement. At last, all motion ceases. At the end of half an hour or so from the time when first stung by the parasite, most such caterpillars are wholly relaxed, soft, and flaccid. When the body is grasped in the middle with the forceps, both ends hang down limply, like flabby sacks full of fluid.

But they are not dead. At temperatures averaging above seventy degrees, they will live in the tubes for from two to four weeks, during all of which interval the heart continues to beat. Under proper conditions of magnification and illumination, this continuous pulsation of the heart muscles is readily observed. Moreover under the stimulation of increased heat and light a week or so after the caterpillars are stung, some slight movement in the poisoned caterpillars may be observed; particularly if they are prodded a little with the blunt point of a forceps. Some silk may be spun occasionally, or a caterpillar may succeed in crawling a little way. Very often the caterpillar lies for days on the ventral surface with the head and the thoracic segments drawn up and back a little, as though the dorsal muscles of that region were in a state of rigor.

Of course such stinging is merely a preliminary to true oviposition, for the eggs are laid externally. Where true oviposition occurs, the feeding Microbracon larvae bring about the death of the Ephestia caterpillar in a week or ten days at temperatures between seventy and eighty degrees Far. Naturally, the death of the caterpillar is hastened by the feeding of the ovipositing Microbracon female which punctures it from time to time with her ovipositor and sucks fluid from the puncture.

OVIPOSITION AND LONGEVITY

I have little to show the effect of oviposition on longevity. In fact, owing to the peculiar feeding habit of the female, oviposition gives assurance of increased longevity. One group, in oviposition for eleven days, lived three months more on honey-water.

When females are not fed at all they live for thirteen to fifteen days or even longer; but this depends wholly on the temperature; for in darkness and at freezing temperatures they live readily for four months or more without food of any kind.

LONGEVITY OF FEMALES FED HONEY

Females fed honey and given no opportunity to oviposit will live for an indefinite number of months. Those given honey and given opportunities for oviposition will live for three or four months; perhaps longer if they are given periods of rest and feeding between periods of oviposition. I have no complete records which will show just how long females may live when given no chance whatever to oviposit. At one time I had no caterpillars of Ephestia kuchniella for two months; but I readily carried the Microbracon females through

this period on honey-water without the loss of a single specimen. They then oviposited as usual and produced abundant progeny.

TEMPERATURE AND LONGEVITY OF FEMALES

One group of females were fed honey-water to repletion shortly after their emergence then placed in darkness at freezing tempertures for four months. They were brought back to the stated temperature, and placed in moderate light. On the following day they were supplied with Ephestia larvae which supply was renewed from time to time as the feeding Microbracon maggots drained the host caterpillars. THE OVIPOSITING FEMALE SUCKS FLUID FROM CATERPILLARS ON WHICH ITS OWN LARVAE ARE FEEDING

Now the females of the little group which were in hibernation for four months are still living, still ovipositing, still sucking fluids from evipositor punctures in the host caterpillars in which their own. progeny are developing. At this writing they have been so confined and feeding for two months and fifteen days.

This peculiar feeding-habit is of the utmost importance to the longevity of the female Microbracon. With her, the odor of the caterpillar, or an antennal stimulus corresponding to an odor, excites first an impulse to sting; then, an impulse to suck fluid from the point stung; finally, an impulse to oviposit upon or more often beneath the flaccid caterpillar.

In general, I find from time to time in tubes where Microbracon females are confined with Ephestia caterpillars, the female parasite sitting quietly on the flaccid prey with mouth-parts pressed into contact with the skin. Apparently the females feed with little or no effort. I have mentioned the great effort made by Pteromalus females in feeding on Pieris chrysalids. With Microbracon juglandis, I note no such violent swallowing of the exuding fluid; and there is of course no such violent muscular effort connected with either oviposition or feeding. The female simply sits quietly on the caterpillar, her mouth-parts in contact with the skin, the tips of the mandibles apparently in contact with the skin. I note very little motion of the mouth-parts at the beginning and at the end of the feeding period.

After many days of starvation, the abdomen of the female is wrinkled and shrunken. The ventral surface becomes carinate, shrunken to the last degree. After feeding on the fluid sucked from the caterpillar, the parasite becomes plump, then engorged. The ab domen fills out slowly until it can hold no more. It is now no longer carinate, but rounded, ovoid, completely engorged.

I will not give here any detailed account of this habit of feeding; for it is in detail similar to the same habit in Meraporus and Pteromalus. In general it is as follows:

Females enclosed in tubes with Ephestia caterpillars sting them into a state of coma as described. Afterwards, for several weeks in the presence of a constant supply of caterpillars, they sting them at intervals with the ovipositor and then suck fluids from these ovipositor punctures until they are engorged with the fluids. Such piercing does not imply oviposition; for the eggs are laid externally.

usually beneath the caterpillars. Finally, the rapid growth of the Microbracon maggots, feeding externally, drains the Ephestia caterpillar completely and causes its death. Thus the ovipositing female obtains a food which sustains her for weeks; probably months, under the most favorable circumstances.

It would be quite possible to have in the laboratory members of several generations of this species, all living, all kept alive by artificial feeding or by the peculiar feeding-habit described.

I should be very sorry to have anyone conclude from the foregoing brief account of this matter of stinging, feeding, oviposition, that I infer any purpose or intention on the part of the female Microbracon.

I think that (1) a perception of the odor of the caterpillar reacts through the nervous system of the Microbracon as the act of stinging. The conditions are now slightly different. We have now a caterpillar with the same odor (?) which is stronger at the mouth of the puncture. The parasite has just finished the act of stinging. (2) Under these conditions the perception of the odor reacts as an impulse to feed. Again the conditions are slightly different: the parasite is engorged with fluid; the ovaries are apparently subject to the pressure of the engorged fluid (?) (3) The perception of the odor now reacts as an impulse to true oviposition.

Now, anyone trained in experimental psychology may easily object to the sketchy looseness of wording in the last paragraph in which the word "tropism" fails to find itself. But let me word the matter again in what I fear is the usual way.

"The female Microbracon uses her ovipositor for three different purposes: (1) as an implement with which to sting the Ephestia caterpillar into such a state of helplessness as will make subsequent feeding and oviposition possible; (2) as an implement with which to pierce the skin of the helpless caterpillar that she may suck fluids from the wound so made; (3) as an implement with which she may deposit her eggs advantageously upon or beneath the helpless caterpillar."

I think the numbered clauses rather neatly descriptive; but are not the implications wholly false? Has the female Microbracon "three purposes"? Then, corresponding to these three purposes I shall endow her with the following groups of concepts: (1) the active caterpillar, the sting, the effect of the poison, the helpless caterpillar; (2) the resistant skin, the pointed implement, the hole in the skin, food to be sucked from the hole, an implied memory of happy larval days when such food was nice; (3) the egg, its nature. its advantageous placing. Are not all these concepts implied in my use of the words, "purpose" and "implement"?

SUMMARY, Microbracon juglandis.

1. Males, in copulation or not, may be kept alive for an indefinite Lumber of months at temperatures close to seventy degrees Far. if fed honey-water. If not so fed, they die in a week or ten days. 2. Females live longer than males under these conditions. Females not fed at all die in from eleven to fifteen days at the tempera

tures quoted. At freezing temperatures they will live without food for four months or more. When fed honey-water, they may live three or even four months in oviposition on caterpillars of Ephestia kuehniella. When fed honey-water and given no chance to oviposit, they will live for an undetermined number of months.

3. The ovipositing female punctures the Ephestia caterpillar from time to time with the ovipositor, and feeds on fluids which she sucks from such punctures.

4. Females will live for many weeks in oviposition on fluids sucked from caterpillars on which their own maggot-larvae may be developing. A little group now under observation have lived thus for seventy-five days and are still alive and active.

SECTION III.-FINAL SUMMARY AND SOME INFERENCES

1 This paper presents (1) an account of a method of feeding and confining certain small parasitic hymenopters and of observing copulation and oviposition in these species, (2) of recording and grouping these observations, (3) of photographing some phases of feeding and oviposition in these species, together with a short series of photographs showing phases of oviposition and feeding in Pteromalus, Meraporus, and Microbracon.

2. It presents certain portions of an incomplete series of observations made by the above methods: the copulation, oviposition and feeding habits of Meraporus sp.; of Tetrastichus sp. nov.; of Pteromalus puparum; of Microbracon juglandis Ashm.; and a few notes on Pimpla sp., and Aenoplex sp.

3. From the notes and observations presented, certain inferences may be made; but these must be most carefully guarded, in that they must be confined with care to those species observed under the conditions named, of food, temperature, light and humidity.

4. In all probability any inferences as to the longevity of the species named under the conditions stated will be found to fall short of the results which might easily be attained by more skillful manipu lations.

This is especially true of the increase of longevity by the habit on the part of the ovipositing female of feeding at ovipositor punctures in the host.

INFERENCES

1. I infer that in nature the species under observation find a varying and irregular supply of food which in its effects on sexual activity and longevity is equivalent to honey-water.

2. That in the laboratory the life of all these species can be prolonged greatly by artificial feeding; that with every one of the species studied the period of copulation and of oviposition can be prolonged in this way from days into months.

3. That the habit observed in Pteromalus and Microbracon females of deriving food from the hosts of their future progeny is of great importance in prolonging the period of oviposition from days. into weeks; often to months in Microbracon juglandis.

4. That in nature, to the species studied, food is of the greatest importance in increasing their longevity and their efficiency as parasites in short, that with these species food bears precisely that relation to longevity which a priori reasoning might lead us to expect.

The results of future experiments should show not only the effect of honey-water on longevity, and on the copulation and oviposition of the species studied in this paper; but they should show something of the effect of sexual activity on the longevity of these species.

It grows clear that to gain a full fruit of such conclusions and inferences, the experimenter must be able to control and to vary at will the conditons under which the experiments are performed. First of all, he must be able to control with perfect sureness the temperatures at which the hymenopters are kept. To control temperatures completely for many months, to vary those controlled temperatures at will, this is the thing desired; but it is a thing to be attained only by means of somewhat elaborate and expensive apparatus.

That is to show conclusively the effect of food on longevity and sexual activity in the hymenopters under observation, and to show the effects of copulation and oviposition on longevity, it would be necessary to have control of the matter of temperature whose influence on activity and longevity is very marked. Otherwise we would get sets of results which would not be comparable; for they would be complications of the effects of two or more sets of influences. Moreover, unless care were exercised we might easily introduce other influential factors, such as light and humidity.

Yet I grow daily more convinced that as a working basis for a knowledge of parasitism we need many exact studies of the effects of those various factors which work together in what we term climate, and of the effects of various kinds of food, on the duration of the period of reproduction in parasitic hymenopters