Kyder.] iJZ [April 7, 



Plate X. 



Fig. 14. Remileuca yavnpni. Spinulated dorsal tubercles of each thoracic 

 segment, final stage. 



15. Gastropacha quercifolia. Scales from dorsal tuft on second 



thoracic segment of the mature larva. 



16. Gastropacha quercifolia. Flattened hairs from the lateral tuft 



of the second thoracic segment of the larva. 



17. Gastropacha americana. Flattened hairs from the lateral tuft 



on eighth abdominal segment of the mature larva. 



Plate XI. 



Fig. 18. Gastropacha americana. Flattened hairs from the lateral tuft 

 on second and third thoracic segments. 



19. Heteropacha rileyana. Flattened hairs from the lateral tuft on 



the second thoracic segment of the mature larva. 



20. Acronycta hastulifera. Flattened hairs. 



21. G lisiocampa americana. Normal hairs, densely spinulated. 

 23. Artace rubripalpis. Freshly hatched larva. Bridgham del. 



Note. — All the figures, except 1 and 33, were drawn by the author with 

 the camera. 



Energy as a Factor in Organic Eoolution. 



By John A. Ryder. 



{Read before the American Philosophical Society, April 7, 1893.) 



The fact that the energy developed by living bodies is correlated with 

 cosmical energj* is now a recognized canon of physiology. To give the 

 proper emphasis to the part played by the energy developed within organ- 

 isms, as a factor in the development of their own forms or morphogeny, is 

 the purpose of the present paper. To define exactly the kinds of energy 

 displayed and the mode in which its effects are produced in particular 

 cases is another part of the subject to be dealt with. The definition of 

 these subjects renders necessary the introduction of a few new terms, in 

 order to avoid awkward circumlocution, to achieve brevity or directness 

 of expression, and to eliminate the riskof indefiniteness in the use of words. 



Haeckel very felicitously proposed the term phylogeny to express the fact 

 that a certain tendency directed the drift or trend of development of a 

 being along a line parallel with that of the series of forms ancestral to it. 

 The being in the course of its development briefly recapitulated that of 

 the ancestral series to which It belonged. This, in substance, is the fa- 

 mous fundamental biogenetic law first suggested by F. Mviller. 



