8 MEMOmS OF THE NATIONAL ACADEMY OF SCIENCES. 



i. To obtain facts regardiug the ontogeny of onr native species and genera which, when added 

 to what we know of the life histories of European, Asiatic, and South American Bombyces, may 

 lead to at least a partial comprehension of the phylogeuy of the higher Lepidoptera, viz, those 

 above the so-called Mici'olepidoptera. 



The transformations of the Bombycine moths are especially noteworthy and useful for the 

 purposes we have indicated, since the group is rich in stem forms, because of its probable 

 geological antiijuity, and because of the remarkable and significant differences presented by the 

 larvic of many of the groups in the numerous successive stages of their larval life, these stages 

 being characterized by distinctive and highly modified shapes, colors, markings, and armatures. 

 These peculiarities, signalizing nearly each stage, were, we believe, evolved in direct response 

 to the changes in their environment, in their mode of life, or to changes in their food plants, 

 and the necessity of being protected through unconscious mimicry from the assaults of insects and 

 reptilian and avian enemies. 



The transformations also afford the clearest possible evidence of the action of what Darwin 

 calls " inheritance at corresponding periods of life," and which Hteckel has tersely designated as 

 " homochronic heredity." 



This fact, moreover, of inheritance at corresponding periods of life throws light on the 

 problem so much under discussion at the present day of the transmission of characters acquired 

 at difierent epochs during the life of the individual. We have devoted a section to a discussion 

 of this question, or rather to a review of some of the facts which strongly suggest the truth of 

 this principle. 



The characters, so unexpected and striking, as for those worked out in Heterocampa biundata, 

 H. guttivitta, and obliqiia, for example, as well as numerous other of the Notodontians and allied 

 families, are plainly enough useless to the insect in the pupa or imago condition, and have evidently 

 been inherited as the result of impressions or stimuli received from without at different periods in 

 the life of the caterpillar alone. 



Such cases occur in many other Arthropods, especially in the barnacles, and in the Decapoda, 

 as well as in the parasitic worms, but the causes can nearly as well be investigated in these insects, 

 which are so accessible. 



Another series of problems is opened up by a study of the mouth-parts of the Bombyces and 

 of their venation, which disclose facts intimately bearing on the genealogy of the Lepidoptera. 



In no other Lepidoptera has the agency of use and disuse, particularly the latter, been more 

 marked. While the mandibles are present in certain of the Tincina and FyraUdiiia, they have 

 totally disappeared from the so-called Macrolepidoptera, or higher and less generalized and primi- 

 tive groups. In the Bombyces, particularly the Saturnians, the maxilla-, owing to disuse, have 

 undergone great reduction, with complete loss of their original function. In another direction, 

 i. e., iu the veins of the wings, there has been a reduction in their number, and this is correlated 

 with their loss of power of taking food, the great but weak wings of these colossal moths being of 

 no use iu seeking for food, which they do not need; as, unlike the swift visitors of flowers, the 

 butterflies. Sphinges, and Noctuids, they are too feeble of flight to sip the nectar of flowers, or 

 too short lived to need any nourishment. 



The geograi>hical distribution of the Bombyces also tends to confirm the view that they are 

 an ancient and generalized group, and to this subject we have given special attention. 



In the systematic portion of the work I have endeavored to arrange the families, genera, and 

 even the species, in accordance with the probable phylogeuy of the group. I have begun my 

 account of the entire superfamily with what I regard as the most primitive family. The seven 

 subfamilies of Notodontians easily fall into this arrangement; it is not difficult to perceive tliat 

 the Gluphisiiuic and Datanin?e are the most generalized, and that the Cerurinre are the most spec- 

 ialized, whether we study the larvte or imagines, though much the clearest light of course is thrown 

 upon the subject by the larva?. It is less easy to indicate the true succession of the genera, though, 

 the way is made very plain iu the subfamily of Heterocampiui?. 



The proper sequence of the species in a large genus is always difficult to make out. It is 

 obvious, however, that the old, unphilosophic method of designating such and such a species as the 

 type of a genus, and then arranging all the others under it, is a thoughtless procedure. Usually 



