112 TRANSACTIONS OF THE ILLINOIS 



produced by this protean agent, so numerous the modes in which it 

 operates, that, like a will-o'-the-wisp, it forever evades our grasp and 

 eludes our search. 



What is life ? is a question which science as yet seems wholly in- 

 capable of answering. Even those who hold that it is of a physical 

 origin are wholly unable to account for its inception, or to explain what 

 it is. Science is, therefore, forced to content herself with studying its 

 works and investigating its operations. These are within her reach, and 

 may, if carefully studied, at length lead to the solution of the great 

 problem, if that solution is within the reach of the human intellect. Its 

 various modes of operating are so many indices pointing towards it. And 

 when we see that the same force can, out of the same earthy materials, form 

 a minute fungus, erect a stately tree, shape a microscopic infusorian and 

 construct the great monster of the deep, we have some conception of its 

 varied powers. 



It is in the lower and more minute animal forms that its modes of 

 operating appear to be most varied; although the individuals produced 

 are less complicated than in the higher and larger forms ; hence, the 

 attention of science has been very largely directed to them of recent 

 years. 



As I have prepared a special paper for the Society for practical use, 

 which will be printed in the proceedings, let us devote the time allotted 

 me this evening to the phenomena of life as exhibited in some of the 

 smaller and humbler animals. 



Let us take, for example, the European cabbage-worm, or larva of 

 Pieris rapce, which has played such sad havoc with our cabbages during 

 the past season, and briefly examine some of the more important points 

 in its life-history, and by comparing these with corresponding points in 

 the lives of other species note the various modes in which life operates ; 

 and at the same time mark the boundary-line of our knowledge in 

 reference thereto. 



At first, as is the case with all other insects, it is an egg — an egg 

 which in this case appears as but a little glittering greenish-yellow speck 

 on the leaf of the vegetable the parent butterfly has wisely chosen as a 

 place where her progeny may find appropriate food ready at hand. And 

 here, at the very commencement of our investigations, an interesting but 

 puzzling question arises. How does the butterfly, whose mouth is 

 adapted only to sucking nectar from flowers, and other liquid sweets, 

 know that her offspring will need food of a different kind ? By what 

 knowledge is she guided to the appropriate plant amid such profusion of 

 vegetable forms? Are we to suppose she retains a remembrance of her 

 former caterpillar life, and the food adapted to that state? Possibly 

 this is the case, and though science may scout the idea, she has no better 

 theory to offer. 



It has been found that the locusts hatched in Kansas and Nebraska 

 will not deposit their eggs on the same ground occupied the previous 

 season, but endeavor, for this purpose, to go back to their native habitats. 



