Mr. A. S. Packard on Aglia tan. I73 



to compare it with Eacles imperialis in its third stage, wliich 

 ]\[r. Poulton could not do for want of specimens. The resem- 

 blance between the two genera at this stage is most striking, 

 although the fully-fed larvaj are so different, Aglia passing at 

 a single moult (the third and last, this larva only having /owr 

 stages) from one family to another ! 



We know of no parallel case, or, at least, of one so very 

 striking and conclusive*. Thus the ontogenetic development 

 of this caterpillar epitomizes that of the two families, whereas 

 that of most Bombyces is simply usually only an epitome of 

 that of a subdivision of a family or of a small group of 

 genera. 



Aglia tau in its third stage differs from Eacles imperialis 

 in its third stage in having a pair of dorsal " horns " on the 

 first and third thoracic segments, E. imperialis having only 

 minute ones on the prothoracic segment, while those on the 

 second thoracic segment are as well developed as those on the 

 third segment ; those on the second segment are minute ; all 

 the " horns " are forked, as in Eacles. The dorsal spines ou 

 the abdominal segments are simple and minute, like those on 

 the second thoracic segment. 



The shape of the head and of tlie anal legs is much as in 

 Eacles, but the suranal plate differs strikingly in being pro- 

 duced into a rather large spinulated spine, a feature not known 

 to exist in any Ceratocampids. 



It should be observed in regard to the large size of the 

 prothoracic horns of Aglia that those of Citheronia regalis are 

 quite well developed, being about two thirds as long as those 

 on the two succeeding segments. 



Upon examining the adult of Aglia I find that its head and 

 antennse are closely similar to those of Hyperchiria io and 

 the Hemileucidge t in general ; the antennge form a close 

 approach to those of R. io, as on careful examination with a 

 good lens a second branch of the pectinations of the male 

 antennge can be perceived ; it forms a long separate branch, 

 but is in the dead and dry specimens very closely appressed 

 to the anterior main pectination. In the venation of both 

 wings Aglia shows a most unexpected resemblance to Eacles 



* Nearly twenty years ago, in 1863, when first beginning my studies 

 on the Bombyces, my attention was attracted to the singular changes of 

 Aglia tau, and I compared the young larva to the full-grown larva of 

 Citheronia regalis, and pointed out that the latter genus was an " embry- 

 onic form, and therefore inferior in rank to the tau moth " {' Amer. Natu- 

 ralist,' June 1870, and ' Our Common Insects,' p. 52j. 



t For the sake of clearness, and on account of the differences presented 

 by the larvre as well as the imagines, I am inclined to provisionally regard 

 this group as of family rank and equivalent to the CeratocampidjB. 



