250 ME. E. B. POULTON ON THE EXTEENAL 



for ilight. The wide individual differences between the females of this species in pattern, 

 shape, size, and character of the fringe are also evidence of recent degeneration (compare 

 figs. 3, 4, 5, & 6, Plate XXVII.). Even stronger evidence is, however, supplied by the 

 closely-allied Hybemia defoliaria, of which the female imagines are usually described as 

 entirely wingless. Minute rudiments of wings can, however, be detected (Plate XXVII. 

 fig. 9). Corresponding to the reduction in the wings, the legs are of great size, being of 

 the utmost importance for locomotion. Comparison between H. defoliaria, H. progem- 

 maria, and the other species of the genus Hybemia, proves that the reduction of the 

 wings has been carried to very different points in species which are nevertheless closely 

 allied. The wings of a female pupa of FL. defoliaria are shown in Plate XXVII. fig. 7, 

 magnified to the same extent as the imago (fig. 9). In spite of the degenerate condition 

 of the imago, the pupal wings are seen to be large and well-formed, and are in fact 

 almost equal to those of the male pupa. The same facts hold for another Geometer, 

 Nyssia zonaria, in which the wings of the female are extremely minute (Plate XXVI. 

 fig. 28), although the difference between the wings of the pupae of the two sexes is quite 

 inconsiderable (compare Plate XXVI. figs. 24 & 25). 



When we compare the pupae of the degenerate Geometers with those of the Bombyces, 

 we find evidence for a more rapid and recent change in the former. Thus the degenera- 

 tion of the latter is of sufficiently long standing to have caused the wings of their female 

 pupae, such as those of Orgyia, Fumea, and especially Psyche, to become decidedly 

 reduced in size. This is evident when we compare the pupal wings of, e. g., the female 

 Fumea (Plate XXVII. fig. 14) with those of the male of the same species (fig. 12). The 

 immense difference between the results of such a comparison and that instituted above 

 in the case of JV. zonaria (Plate XXVI. figs. 24 and 25) or H. defoliaria proves that the 

 degradation of the latter is of far more recent date. 



The comparison between pupal and imaginal wings in species with degenerate females 

 indicates that Professor Moseley's conclusions require some modification ; for in some 

 of the species the pupal organs have shrunk as the corresponding imaginal organs have 

 diminished, although the former have changed at a much slower rate. Hence we are 

 driven to conclude that the particular shape and size of a pupal organ, which at any one 

 time fits an imaginal orgau developed within it, will not be retained indefinitely upon 

 the shrinkage of the latter, as Professor Moseley was led to believe from his observations 

 upon the antennee, but that the pupal organ will also eventually become smaller. At any 

 rate, this has been the case with the pupal wings. I do not think that at present there is 

 any evidence for believing that the female pupal antennae have yet shrunk like the wings ; 

 for the former, although smaller than the same organs in the male pupa?, may nevertheless 

 have been at no time larger than at present. Such a conclusion is supported by the argu- 

 ments in the last division of the subject, in which it was shown to be very probable that 

 the male imaginal antennas have increased as the female organs have diminished, so that 

 the pupal organs of the former must have undergone recent increase, while the female 

 pupal antennas may indicate the size of these organs in both sexes, before degeneration of 

 the one, and concomitant development of the other, commenced. Or, considering how 

 very common it is among moths for the male antennte to be more developed than those of 



