246 MEMOIRS NATIONAL ACADEMY OF SCIENCES. vol. xii, 



and appearance of Attacus. It differs from Samia in the rather slender body, the decidedly 

 longer tubercles, and the slighter, shorter bristles arising from them, and in coloration by the 

 pale lemon-yellow skin, with the conspicuous black spots, and the beautiful turquoise-blue 

 markings, as well as the peculiar soft white bloom on the skin. How far this style of ornamen- 

 tation adapts it to its native Asiatic food plant we do not know. 



Recapitulation of the more Salient Ontogenetic Features. 

 A. Congenital Features. 



1. Hatched with large, well-developed setiferous tubercles; but the bristles not bulbous 

 in stage I. 



2. The body pale, but the tubercles dark, and besides these intertubercular conspicuous 

 black spots are present in stages I to V. 



3. The homologue of the "caudal horn" is double, bearing four bristles on each side. 

 The difference between the larva of the first stage and the last, unusually slight compared 



with Samia and Callosamia. 



B. Evolution of later Adaptational Features. 



1. The tubercles become pale at tip in stage III, and those of the two dorsal rows of the 

 thoracic and last two abdominal segments become slightly larger than those of abdominal seg- 

 ments 1 to 7, in stage III. 



2. Differences in coloration appear in stage IV, the head, prothoracic ami last two abdomi- 

 nal segments being honey-yellow, thus contrasting with the whitish body, with its whitish bloom, 

 which also appears in this stage. 



3. Further changes in color appear in the last stage, the ends of all the tubercles becoming 

 pale bluish, and the edges of the suranal plate and anal legs being a rich turquoise-blue. 



4. In the last stage a very slight difference in the size and shape of the thoracic and the 

 last abdominal tubercle. 



5. The tubercles on the suranal plate become reduced to low bosses, without bristles. Thus 

 Philosamia cynthia is a decided step in advance of Samia, and appears to be a later formed genus. 



Comparison between the larva of Philosamia and Callosamia. — The fully fed larva of Philo- 

 samia cynthia is in the shape of the head and body, and in the shape of the tubercles with which 

 the latter is armed, more allied to Callosamia than to Attacus, although the imago is perhaps 

 as near the latter genus as to Callosamia. The head of the larva of Philosamia is almost identical 

 with that of Callosamia. The nearly obsolescent tubercles on the prothoracic segment have 

 about the same degree of degeneration in Philosamia as in Callosamia, but the former differs in 

 the fact that the lateral tubercles hi all three thoracic segments are well developed, and end in 

 a head armed with four spines, as in Samia (S. cecropia), while the tubercles are as well devel- 

 oped on the abdominal segments as on the thoracic. The thoracic tubercles also are no 

 more differentiated than the abdominal ones. Philosamia also differs from Callosamia in the 

 12 rows of black spots along the body. The larva of Philosamia is thus seen to be intermediate 

 between Samia and Callosamia, but the moth is apparently intermediate between Callosamia 

 (C. angulijera) and Attacus. 



The head and the shape and size of the body of the larva are like those of Callosamia, but 

 in its secondary adaptive generic characters it retains a resemblance to Samia. In a syste- 

 matic classification, then, we had better adopt the imaginal characters rather than the larval, 

 the latter being so much more plastic and more readily influenced by changes in the mode of 

 life and by differences in the food. In its earliest larval stages, the insect is certainly more 

 like Samia cecropia than Callosamia, but still even in these stages Philosamia is more advanced 

 than Samia, which in its earliest larval stages, especially in the possession of long bristles arising 

 from the short tubercles, intergrades with or is closely allied to the fully grown larva of Saturnia 

 carpini; and in the imaginal characters Samia is nearer the ancestral form Saturnia (in the 

 restricted sense) than to any of the other Attaci. If we do as we should do in locating Philosa- 

 mia in its proper taxonomic position, we shall not err greatly in placing Philosamia much abovo 

 cecropia, and on the whole near Attacus. 



