THE SENSE CONTItOLLlNG INSECTS IN" PXiG-DKPOSlT. 67 



naplitliaiine,* carbolic acid, gas-lime, and bisulphide of carbon. That 

 these and similar substances have been successfully used in preventing 

 insect attack is undeniable, resting, as the claim docs, on the authori- 

 tative testimony of some of our best writers and experimenters in 

 economic entomology. 



How do they prevent egg-deposit — They do so, by giving out 

 an odor overpowering that of the plant (or animal), thereby prevent- 

 ing its recognition bv the insect. 



For the acceptance of this proposition, it is necessary also to accept 

 the following: Insects, as a rule, are guided in the deposit of their 

 eggs, not by the sense of sight, but by that of smell. A somewhat ex- 

 tended consideration of this view seems desirable, before proceeding to 

 its practical application. The idea is a popular one, that most of the 

 moths and beetles, and many of the insects that attack vegetation, se- 

 lect by means of sight the particular plant upon which to place their 

 eggs. Their marvelous compound eyes, consisting of hundreds and 

 even thousands of separate lenses, even to the number of 34,000, as in 

 the eye of the butterfly, have been cited as a wonderful provision in 

 nature, to afford that acuteness of vision which was needed in their 

 selection of the proper plant upon which to oviposit. While sharing 

 in this belief, I had often wondered at the incomprehensible acuteness 

 shown by an insect in the discovery of the particular species of plant 

 up >n which alone the young caterpillars proceeding from its eggs 

 could feed, — in the discovery of a single individual of a rare species 

 occurring in a certain locality, and growing in such a manner as effec- 

 tually to hide it from human observation. When its range of food- 

 plants extends beyond a species to all the members of a genus, how 

 could it detect all of the often greatly differing forms? When a still 

 broader range embraces the several genera of an extended order, a still 

 greater A^ariety of forms are jjresented, which the rude insect brain 

 must group and classify, and claim within its province. How amaz- 

 ing such knowledge without j^revious instruction. It had no parents 

 living, as in the class pf vertebrates, which might teach it by example. 

 It liad no ancestors a whit wiser than itself from which to learn. The 

 deposit of the e^g in its proper place may have been but the second 

 voluntary act of its imago life, regarding that of flight for the purpose 

 as the first. Perhaps a plant from some distant shore, of which not 

 one of its ever so remote ancestry could have had any knowledge, is 



*Naphtbaline is one of the products of the distillation of coal-tar, which, together with 

 the other two products, anthracine and benzole, is largely employed in the manufacture of 

 aniline colors. One hundred pminds of coal-tar gives from six to eight pounds of naphtha- 

 line, from one-fourth to one-half pound of anthracine, and from two and one-half to three 

 pounds of beniole. 



