246 ME. E. B. POULTON ON THE EXTERNAL 



in the male for sexual purposes, but must have been retained in the male and degenerated 

 in the female. Further, it seemed to me that in the form of the pupa of Lepidoptera, 

 and probably in Coleoptera and other forms also, many facts of important ancestral 

 significance might be found preserved. The integument of the pupa, requiring for 

 purposes of protection to be hard and rigid, when once it had assumed a particular shape 

 suited to the contours of the body of the original ancestral insect, would retain that form 

 indefinitely, although the shape of the several parts of the imago formed within it might, 

 by the action of natural selection on it when in the free moving condition, alter consi- 

 derably. It appears to be of no detriment to the development of the legs and the 

 antenna? of the imago that their pupa-cases are far too big and do not fit. I concluded 

 from the observations on Saturnia that probably members of the Saturniidte must exist 

 with well-marked pectinated antennae in both sexes. I did not in the least know that such 

 was the case, but soon saw that it is so on looking at Westwood's drawers of insects. If 

 you think well to refer briefly to any of the above I shall be much obliged. It was in 1871 

 that I began to look into the matter, but it was cut short by my expedition to Ceylon. 

 Wishing you all success, " I remain, &c, 



" H. N. Moseley." 



Other parts of this paper, in addition to the section upon antennse, bear witness to the 

 general applicability of Professor Moseley's conclusions to the systems of organs which 

 can be traced in the external morphology of Lepidopterous pupae. At the same time it 

 will be shown that the shrinkage of a part in the imago ultimately leads to the shrinkage 

 of the corresponding part in the pupa. The latter change, however, keeps behind the 

 stage of degeneration reached by the imago, so that an earlier condition of the imaginal 

 organs can often be traced upon the pupa. 



Directly my attention was called to the point I looked out for similar facts in many 

 species of pupae, and always with the same results. When there is much difference 

 between the antennae of male and female moths, there is always less difference between 

 the antennae of the sexes of their respective pupae. I found this to be the case with 

 pupae of the genus Smerintlms, where the difference between the imaginal antennae is not 

 excessive, and in pupae such as Pi/gcera bucephala, Cerura vinula, and Orgyia antiqua, 

 in which the difference is much greater. In all cases we have evidence for comparatively 

 recent increase of the sexual differences in the imago state. 



A comparison of figs. 1, 2, 3, and 1 on Plate XXVI. will show the evidence upon which 

 Professor Moseley relied for his conclusions. But the same conclusions are further 

 supported by a more minute examination of the antennae of the female imago. If these 

 have undergone comparatively recent degeneration, we should expect to find great indi- 

 vidual difference in the degree to which degeneration is carried, and we should expect to 

 find traces of structures which were necessary for former functional activity. Figures 5 

 and 6 (Plate XXVI.) prove that the degree of degeneration varies greatly in different 

 individuals (see description of figures), and that rudimentary sensory hairs are scattered 

 over the reduced equivalents of the highly-developed rami of the male organ. 



Corresponding facts come out still more clearly in the European Aglia tau, in 



