294 



SCIENCE- GOSSIP. 



skilfully it is unable to assist others. Observe, too, 

 that only the larvae of the lion-ant construct these 

 traps. The full\' developed insect has other modes 

 of existence and different oi'gaus. The lion-ant 

 absolutely loses its former instinctive habits, 

 because it has no further use for them. These 

 remarkable creatures have instinctive habits x^ecu- 

 liar to the several metamorphic states. Let those 

 vs'ho can explain how these insects, arising from 

 the same source, and having regard to the several 

 forms through which they pass, can adapt to each 

 state new habits and modes of living, according to 

 the requirements of these several states. I have 

 not met with any modern theories that will account 

 for their absolute uniformity of action. 



The voracity of caterpillars of herbivorous 

 insects is well known. From the time of their 

 birth until they evolve from the larval state is a 

 long uninterrupted period of browsing. They are 

 very numerous, and anj' attempt to destroy them 

 usually ends in failure. Many do perish, but the 

 number is small compared with the hosts that 

 escape to become mature insects. What chiefly 

 concerns us is the apparent sagacity shown by the 

 mother insect in depositing her eggs on a particular 

 plant. The common white butterfly, Pieris brassicae, 

 for instance, deposits her eggs on plants of the 

 cabbage family. The Pieris herself does not feed 

 on that plant ; her food is the nectar found at the 

 base of the corollas of flowers. She cannot " know " 

 what food her young brood will require when they 

 emerge from the egg. Why she should so un- 

 erringly select a member of the cabbage family, in 

 preference to other plants in the vicinity, is at 

 jjresent entirely beyond our limited means of 

 observation. Her organic structure does not help 

 us, and we must leave the problem. We shall find 

 many of these difficulties in natural historj^ ; but 

 it would be unphilosophical to despair of ultimate 

 solution, and we should therefore keep our minds 

 in a state of judicious suspense, hoping that the 

 patient research of the future will throw light on 

 the subject. 



The caterpillar has many enemies, and of these 

 none, perhaps, more unremitting than the ichneu- 

 mon flies. They are four -winged insects, of 

 numerous species, which feed upon honey. The 

 females a-e furnished with an ovipositor, proceed- 

 ing from the posterior part of the abdomen, often 

 of great length. The ovipositor is a hollow tube 

 pointed like a needle, and is used to insert its eggs 

 deep into the bodies of the larvae of other insects, 

 in the abdominal cavity of which the footless larvae 

 live parasitically, and often change into pupae. 



The sole object of the life of the perfect female 

 ichneumon fly would appear to be to discover a 

 proper nidus for her eggs. She hovers like a bird 

 of prey over a plant, and as soon as she discovers 

 a caterpillar, darts down upon it and binds it 

 fast with her feet. The needle-pointed ovipositor 

 is inserted into the body of her victim, and at 



the same time an egg slips along the oviduct and 

 passes into the wound. This operation is repeated 

 over several parts of a caterpillar's body. Fre- 

 quently the laying commences in the body of one 

 caterpillar, and is finished in that of another. The 

 ichneumon lays a number of eggs proportionate to 

 the size of her victim's body. The host cater- 

 pillar's body is destined to serve as food for the 

 larvae as soon as they are hatched, and a sufficient 

 quantity of nutritious material is necessary to 

 ensure complete development. The ichneumon 

 fly, by thus distributing its eggs, would appear, to 

 a casual observer, to possess ceitain properties of 

 mind. The conception of proportionate parts is 

 an involved mental pi'ocess, and implies a superior 

 intelligence. Does, however, the ichneumon per- 

 ceive — and this is the crucial point — the purposes 

 of that distribution ? For my own part, I un- 

 hesitatingly reply in the negative. The brain, if 

 one may be permitted to speak of an insect's brain, 

 fails to justify such a lofty claim. When referring 

 to an insect's brain, we allude to the entire nervous 

 mass rather than to one specialised organ. An 

 insect may be said truly to have many brains : but 

 if we insist upon finding one brain, the first ganglion 

 in the spinal marrow may be so regarded. The 

 functions of that brain, however, are merely to 

 control the corporeal activities. The insect has 

 no organ analogous to the larger brain in the 

 higher animals, and in which the intellectual 

 powers are located. The ichuev;mon cannot, there- 

 fore, be said to cogitate, and its remarkable 

 properties must, for the present, be ascribed to 

 some unknown cause. 



Equally interesting are the larvae, which in de- 

 voui'ing the caterpillar strictly abstain from inter- 

 fering with, the vital organs, the loss of which 

 would mean the certain death of their victim. 

 In the interests of the larvae, the caterpillar host 

 must live until they have attained complete de- 

 velopment. At the last moment only, when they 

 have reached the end of their larval state, are the 

 vital organs consumed and the caterpillar put to 

 death. The death of the one and the complete 

 development of the other are simultaneously 

 effected. 



At this point we may revert to the egg-distri- 

 buting properties of the ichneumon fly, and the 

 no less remarkable instincts of its larvae. It has been 

 argued that the ichneumon, in the ca^e of a small- 

 sized caterpillar, may limit the distribution of its 

 eggs, because it meets with obstruction and can 

 find no farther space. If this were sc, irregularities 

 would ensue ; but no one has ever known the 

 ichneumon to make a false calculation that would 

 involve the death of its young. This would fre- 

 quently happen were the ichneumon guided by no 

 other cause than obstruction and an absence of 

 space. Any irregularity or uniformity, a sine qua 

 non of instinct, would be as hopeless as the pro- 

 duction of the "Iliad" of Homer by a chance 



