28 3IEM0IPtS OF THE NATIONAL ACADEMY OF SCIENCES. 



Neuroptera, Coleoptera, Mecopteia, TiicLoptera, Lepidoptera. Diptera, and Hymeuoptera, ^yhel■e- 

 there are so many and perplexing cases of incougnieiice or divergence in larval forms whose 

 parents are very closely allied. 



It is worthy of notice that iu respect to Diptera the veteran dipterologist, Baion li. von Osten 

 Sacken, remarks of the nemocerous tlies: "An arrangement of the imagoes based upon such prin- 

 ciples will of necessity be justitied by a more or less tangible correspondence in the characters of 

 their larva'. This structural correspondence, this parallelism of larva' and imagoes among the 

 Nemocera, sufters, as far as I know, but one exception, Mijcetohia puUlpes and Khyphus. In both 

 almost identical larvse produce flies belonging to different families." (Berliner entomolog. Zeit- 

 schrift, r.d. xxxvii, 1892, Heft iv, p. 418.) In the copy kindly sent me by the author a second 

 case of Anopheles and Dixa is mentioned in the printed copy, but struck out by the author iu the 

 emended copy. 



Everyone is familiar with the fact that there is a nearly similar incongruity between the larvoe 

 of the Muscid;e and the flies. Many new facts bearing on this subject appeared iu I'ortchinsky's 

 article on the habits of the necrophagous and coprophagous larvre of Muscidie, of which an English 

 abstract by Baron E. von Osten Sacken appeared iu the Berliner ent. Zeitschrift for 1887. After 

 speaking of the wonderful power of adaptation of these larva; to their environment, he states: 



Distinctly related species belonging to different genera issue from larvie almost indistinguishable from each 

 other. And again closely related and almost indistinguishable imagoes, species of the same genus, differ in their 

 ovipositiou (size and number of eggs), and their larv;e follow a different law of development (as to the degree of 

 maturity the larva reaches within the body of the mother and the number of stages of development it passes through). 



In one ease even {llusca con'iiia) larva- of the same species were found to have a different mode of ilevelopmeut 

 in northern and southern regions of Russia. 



Here also it is evident that the cause of the incongruity is due to the fact that the larva-, for 

 the time being different animals from the adult, are moditied by their environment, the similar 

 surroundings and habits of the larva', of quite different genera causing the larva; externally at 

 least to closely resemble each other. Whether they are so similar in their internal organs remains 

 to be seen. Dr. C. W. Stiles, who has studied so carefully by microscopic sections tapeworms of 

 externally similar form, and which can not be separated by external characters, tells me that the 

 internal organs seem to aftbrd excellent specific and generic characters. 



Lepidopterists in general do not hesitate to base their systems of classification on the larval 

 as well as adult features. They iu general regard their systematic arrangements of the imagines as 

 more or less provisional, and all acknowledge that it is immensely satisfactory, even after they are 

 pretty well satisfied with th eir arrangement of the adults of a group, whether a genus or family, 

 to work out the larval stages and to check their classifications based on adult features by the 

 larval characters. In many cases they may bo led to change the position of a species or genus, 

 or to split t;p a genus or species. 



But, after all this, the tact that so umny larvii^, even in the same group, are hatched with such 

 different shapes and characters; the fact that some are so much more simple and primitive than 

 others, ope;is up most perplexing yet interesting questions and problems. We may, however, be 

 able to solve these, and in the present group of Bombyces it seems to us that the different larval 

 forms, some primitive and generalized and others more or less modified or specialized, give clues 

 to the phylogeny of the groups which we confess we had not expected. 



And in this memoir we have endeavored, though often it is mere guesswork, to drop the old- 

 time method of putting the type species first and then ranging the others after it in an ill-assorted 

 group, and have attempted to begin with what has seemed to us to be the ancestral form of the 

 grcup, following with the later forms. This can be best accomplished by taking into consideration 

 the caterpillar, beginning with the generalized forms and ending with the later more modified 

 or specialized forms. In such a large genus as Heterocampa this is not diflicult to do. For 

 example, as we shall see hereafter, the larva of H. manho is as simple and generalized as any, 

 while that of H. unicolor is the most modified, with its semi-stemapoda, from which Macrurocampa, 

 with its fully formed st enmpoda, may.ha ve descended. And then, while Cerura, with its stemapoda 

 alike in all the species, is often or generally placed first iu the group, it is evident that it was 

 descended from some Heterocampa-like form through Macrurocampa. Aided by our knowledge of 



