256 HABITS AND INSTINCTS IN LEPTINOTARSA. 



less fundamental characters which are usually associated with this rapid 

 development of new forms. 



The only other habit that can claim classification as a protective one has 

 already been discussed. It is the habit which the larvae of undecimliueata, 

 diversa, and signaticollis have of covering themselves with the trichomes of 

 their food plant. This, however, is an extremely passive habit, which is due 

 solely to the facts that the beetles feed upon species of Solarium that have a 

 rich development of trichomes on the under sides of the leaves, and that the 

 young larvae are supplied with spines in greater or less number and integu- 

 mentary glands which secrete a sticky fluid, so that the trichomes become 

 attached to the larva as it moves around upon the leaf. This habit is found 

 in the first two instars only, when the larvae are small and not active ; as they 

 become larger, however, the trichomes, even when they do adhere to the body, 

 are not apt to remain there, because of the more active movements. The effect 

 upon the young larvae is to produce a rather efficient disguise. 



This habit or protective device is, however, accidental, because whenever 

 any of these beetles happen to feed upon a species of Solatium which does not 

 have the dense deposit of trichomes, they thrive just as well, both in nature 

 and experiment. Hence this apparently protective habit is simply the acci- 

 dental accumulation of trichomes upon the body which is found in these three 

 closely related species, because they all feed upon identical or closely related 

 food plants. As far as I can discover, the habit has neither utility to the spe- 

 cies nor has it injurious effects, and therefore it can not become a means of 

 selective action until the time shall arrive when it is either of advantage or 

 disadvantage to the species. 



The three great groups of habits in these beetles have been examined not 

 with the purpose of an animal psychologist, but in order to learn what part 

 they play in the life of these beetles, which are being used as material for the 

 study of animal evolution. The reader must not, therefore, be greatly disap- 

 pointed if he fails to find herein the "final solution and explanation" of the 

 habits of these insects. In this paper an insight has been gained into the part 

 played by these various habits in the economy of the species, and to a certain 

 extent into the manner in which these habits may act in the evolution of the 

 genus. It has been clearly shown that some of the habits have a decidedly 

 selective influence, but in all the habits discovered this influence is exerted in 

 the direction of conservatism, and is of no use whatsoever in the preservation 

 of a newly-appearing variation, no matter how useful it may be to the species. 

 This conservative tendency, however, is a highly important factor in keeping 

 the species true to the modal type, and may thereby be a far greater force in 

 evolution than it would be if it concerned itself with every little variation pos- 

 sessing a slight degree of utility to the species. I am strongly of the opinion 

 that when we are really better acquainted with the process of natural selec- 



