CLASSIFICATION OF INSECTS. 5 



imaginal form evolved directly from these initial stages. In tin- 

 fly, however, as in other speciali/ed insects we find the- newly 

 hatched larva almost destitute of morphological indications of 

 most of the appendages which reappear much later in larval life 

 as histoblasts that represent the rudiments of the imaginal 

 appendages. 



However, we may regard the interpretation of the biogenetic 

 law as applied to other animals, it is evident that many insects 

 exhibit a very distorted development when viewed from this 

 standpoint. This matter has been treated already by Janet in 

 his "Ontogenese de 1'insecte" ('09). The taxonomist, who is 

 continually brought into contact with the permutations of 

 various single characters, soon begins to regard species as made 

 up of, or at least most easily definable, by series of single clear- 

 cut characters. His attitude is also closely parallel to that of 

 the geneticist who finds that he must attack his problems through 

 the behavior of unit characters. Cope ('95) early called atten- 

 tion to the dependence of the taxonomist upon single characters 

 in his discussion of the biogenetic law as applied to vertebrates. 



In a series of papers, which have been gathered together in 

 his "Biologic Generale" ('n), Giard ('92- '05) described certain 

 peculiar phenomena of development which he termed poecilogony. 

 Among several widely separated groups of animals, certain 

 isolated species show modifications in their ontogeny whereby 

 two widely different types of development give rise to individuals 

 belonging presumably to the same species. This appears fre- 

 quently to be independent of any alternation of generations and 

 occurs in forms of many well-known genera. Giard regards 

 some cases of pcecilogony from the standpoint of their probable 

 origin as seasonal poecilogony, geographic poecilogony or as 

 ethological poecilogony. How far these phenomena can be 

 regarded as the expression of a single principle is somewhat doubt- 

 ful, since the significance of the alternation of generations that 

 occurs to such a widely different extent in several groups of 

 insects is by no means clear. Also, de Meijere ('10) and others 

 have shown that the polymorphism of certain Lepidoptera follow r s 

 Mendel's law in inheritance and that the characteristics of the 

 different forms of female in Papilio behave as unit characters. 



