50 MEMOIRS OF THP: NATIONAL ACADEMY OF SCIENCES. 



funiily is a composite oi- synthetic one, embracing forms both leading- up to and iuchidiiig the 

 Sphingida-, all Itound together liy genetic ties. A.s there are already too many moditications of 

 the names Sphingidw and BombycidiV, we venture to hope that the name we here propose 

 may be accepted by entomologists. For all the syssphingine families, below Sphingida\ I pro- 

 pf)so the name Pr<if<is-phhnih)ii. 



XIII. ORIGIN OF THE SYSSPHINGINA BY BOTH CONTINUOUS AND DIS- 

 CONTINUOUS EVOLUTION. 



The results of our studies have taught us that two modes of evolution have been at work in 

 the origin of the family of Sphingid.v. First, there was, due to a change of habits, a gradual, 

 continuous process of progressive modification of the small-headed, shorttongued. thick-bodied, 

 sluggish, or nearl\- flightless Saturniides by way of the Ceratocampina^ into a Cressonia-like 

 form. This process of change and adaptation to new conditions of life went on for perhaps 

 many centuries or thousands of generations. At length there was a sudden acceleration or 

 revival of growth and development in those partly atrophied organs like the maxillte, etc., which 

 l)ecame restored to the functions enjoyed by the more active ancestors of the saturnian 

 .subphylum. and at a critical period, after one consisting of long preparatory but slight changes, 

 a p'-r salttim movement or leap occurred, and as the result of this rapid assumption of a new 

 character, which we call an aberration, sport, or mutiition, the tubercle v of the larva- became 

 shifted from its position in the ceratocampid larviv to what it is in Cressonia, (.'eratomia. and the 

 other Sphingida thus far examined, and there also appeared an additional radial vein. 



This has been the case with the origin of the genera not only of this group, but this process 

 of frequent rapid evolution takes place in the organic world in general. An example is the 

 differences between Adelocephala and Anisota, the larva' of the latter genus differing so 

 remarkal)Iy from those of the stem-form in the return to the primitive separate tubercles // of 

 the eighth abdominal segment and the reduction in the ai'mature, that only a single pair of 

 thoracic horns are left. 



Doctor Dyar " has called attention to the discontinuous evolution of a wart bearing hairs 

 from a simple .setiferous tubercle, stating that •• we do not tind a series of intergrading forms 

 between the single-haired tubercle and the many-haired wart, though both may occur in different 

 genera of the .same family.'" The wart-like tubercles which characterize the Saturniidie are 

 apparently suddenly produced characters; also the peculiar branched tu))ercle spines of the laival 

 Hemileucida'. and certainly the lateral eversible glands which are peculiar to and diagnostic of 

 that family. In fact the fusion of the two tubercles / on the eighth abdominal segment of the 

 Syssphingina is a ca.se of more or less sudden or rapid evolution. Thus the discovery that Rom- 

 bycidse {Bomhyn- inori), Brahmaida". and Endromix rers/colora (Endromidtv) all have in the first 

 lai'val stage warts bearing several hairs proves that they belong to a different phylum from the 

 Svssphingina and should be associated with what we would call Syiii}jomh)/cina. including the 

 Eupterotida. Lasiocampida, and Liparida. these families, perhaps, having arisen from the noto- 

 dontian groups Apatelodina and Ichthyurina (Melalophina). 



We hence infer that those absolute characters which distinguish or are diagnostic of lepi- 

 doptei'ous families, however slight or trivial in them.selves, are sudden acquisitions, due perhaps 

 to comparatively sudden changes in the conditions of life, involving new needs, the formation of 

 new habits, different food plants, etc., or some unknown stimulus. If this be the case, then the 

 diff(M-eTit family groups, as well as generic groups in the Lepidoptera, have arisen as sudden 

 depaitures or changes or divergent steps in the course of what otherwise would be a .slow, evenly 

 graduated process of progressive development. If this is the case with Lepidoptera so it is in 

 other orders of insects and other arthropodous phyla, and, indeed, throughout the organic world. 

 For example, the birds with more or less suddenness diverged from the reptilian line of descent; 

 mammals with two condyles originated by a process of rapid evolution from reptiles with but 

 one condj-le, and so on. 



"Annals N. Y. Acad. Sc, viii, May, 1894, p. 196. 



