MORPHOLOGY OF THE LEPIDOPTEKOUS PUPA. 259 



imaginal antennae during development and just before emergence. The character of the 

 surface is only indicated on the left side. 



Fig. 9. x 7. The left antenna of the male imago of Aglia tau, as seen from above and behind. The 

 fine sensory hairs are not indicated. The organ is seen to be even larger than that of the 

 male S. carpini (fig. 3) . The enormous size of the imaginal organ corresponds with that of 

 the pupal organ within which it is developed (fig. 7). 



Fig. 10. X 7. The left antenna of the female imago of Aglia tau, as seen from above and behind. Just 

 as the male organ is larger, the female organ is smaller than in S. carpini (fig. 4), indicating 

 that the degeneration of one sex has gone hand-in-hand with an increase in the powers of the 

 other. The recent date of the degeneration is well seen when we compare the size of the 

 imaginal organ with that of the pupal organ within which it is formed (fig. 8) . 



Fig. 11. X50. The terminal part of one of the posterior rami from a joint of the antenna of the male 

 Aglia tau. Each joint bears two pairs of rami (fig. 9), of which the posterior are larger and 

 more complex. The figure shows the long curving sensory hairs and the three terminal 

 bristles. Both hairs and bristles are foreshortened. 



Fig. 12. x 50. The terminal part of one of the anterior rami from a segment of the antenna of 

 the male Aglia tau. The figure shows the long curving sensory hairs, which are turned 

 towards those of the posterior ramus of the segment in front. The arrangement of the 

 rami is shown in fig. 9, where they are seen to form pairs on each side of the middle line, 

 made up of the anterior rami of one segment placed opposite to the posterior rami of that in 

 front of it. The length of the sensory hairs is more fully shown in fig. 12, because they are 

 seen from the side. Figs. 11 and 12 show that the male antenna of Aglia tau is extremely 

 complex, and the arrangement is such as to render it an unusually efficient organ for sifting 

 a large quantity of air, so that the faintest trace of odour may be detected. 



Fig. 13. X 50. Two of the most fully developed segments from the right antenna of the female Aglia 

 tau, seen from below and in front, in such a position that the rudimentary sensory haii-s of the 

 posterior inferior border are in profile. The male antenna is more complex than that of 

 S. carpini ; but this figure shows that the degeneration of the female has been carried far 

 beyond the point reached by the female S. carpini (compare figs. 5 and 6). The rami represent 

 the posterior pairs of the male organ. Those of the posterior inferior border possess two 

 terminal bristles, while those of the other border only possess one. The difference between 

 the size and arrangement of the sensory hairs in male and female is very striking. 



The arguments as to the recent date of the degeneration of the female, derived from S. car- 

 pini, are thus confirmed and extended by an examination of Aglia tau. 



Fig. 14. x 9. The outline of the left pupal antenna of the male Orgyia antiqua. 



Fig. 15. x9. The antennae, limbs, &c. of the female pupa of Orgyia antiqua. The pupal cuticle had 

 been mounted for the microscope, so that the structures were somewhat flattened. The an- 

 tennae are seen to be broad and well developed, although much smaller than those of the male. 



Fi". 16. x 9. The antenna of the male imago of Orgyia antiqua, showing the great size and complex 

 structure. The development of the organ corresponds with that of the pupal antenna, as 

 in the males of Aglia and Saturnia. 



Fig. 17. X 9. The antenna of the female imago of Orgyia antiqua, showing an extremely degenerate 

 condition. As in Aglia and Saturnia, the corresponding pupal organ has a size which is utterly 

 disproportionate to that of the thread-like and rudimentary structure developed within it. 



Fi°-. 18. X 50. A segment from the middle of the antenna of the male imago of Orgyia antiqua. 

 Although inferior in complexity to the correspondmg organ of Aglia and Saturnia, the 

 structure is extremely elaborate. The rami, of which there are a single pair on each segment, 

 are seen to be abundantly covered with sensory hairs, and to possess three terminal bristles. 



