DIMORPHIDI. 231 



supplementary suggestions as to the relationship of Dimorpha with 

 the Sphingo- Saturniid - Lachneid stem on characters, other than 

 imaginal, are offered by Bacot, who writes : 



Egg : Characters offered by shape and similar proportions between the three 

 diameters. Larva : Position and development of tubercles ; shagreen development ; 

 coloured bases of secondary hairs ; their distribution in relation to coloured stripes ; 

 the caudal horn on 8th abdominal segment ; oblique stripes. Cocoon : Structural re- 

 semblance to those of Eumorpha (Choerocarnpa) elpenor, Aglia tauand Caligula jap - 

 onica *. Pupa : General resemblance to that of Aglia tan, but without the recurved hooks 

 or spines on the anal armature, in this respect the pupa of C.japonica* is nearer to that 

 of D. versicolora, as its cremaster is very broad and spade-like, and the recurved hooks 

 are restricted to a few at either corner of the anal extremity. Among the Sphingids 

 both Eumorpha and Smerinthus show resemblances, the former in the development 

 of its anal armature and dorsal spines to enable it to emerge from cocoon ; the latter 

 in the anal armature, rugosity, and solidity of structure, characters which it possesses 

 in common with Citherortia. 



The young larva in its first instar shows Lachneid and Saturniid 

 rather than Sphingidf affinities. The dorsal and lateral tubercles 

 of the abdominal segments, with the exception of ii, being composed 

 of groups of from two to four hairs, the chitinous bases, of which, 

 in i and iii, conjoin to form a single wart, but in the case of iv and 

 v the bases are not as a rule joined. In development, i and iii agree 

 both with Saturniid and Lachneid forms, although they are more 

 primitive than in any larva of the former group that I have yet 

 seen, and iv and v are more primitive in character than in any 

 Lachneid larva with which I am acquainted. On the other hand, ii on 

 abdominal segments is single-haired, and on the meso- and meta- 

 thoracic segments there are only three tubercles present on either 

 side above the ventral area, all of which are wart-like and bear 

 several hairs. The dorsal one is probably i + ii, or possibly it is 

 i alone, ii having been lost ; iii is in the usual supraspiracular position ; 

 the subspiracular is almost certainly iv + v. It would appear, there- 

 fore, on larval evidence, that Dimorpha had specialised away from the 

 Sphingid stirps in respect of the multiplication of hairs on larval tuber- 

 cles, and that its similarity of coloration, &c, in later instars, is due to 

 similarity of needs, habits and environment acting on a but slightly 

 altered constitution. The fact that in some characters it is behind the 

 Lachneids, while in others [loss of ii (or conjunction of ii with i) 

 on meta- and mesothorax] it has advanced further than Aglia tau 

 in the Saturniid direction, seems to point to its having branched 

 from the Saturniid stirps ; but the egg would seem to contradict 

 this unless we conclude that the solid opaque and porcelain-like 

 characters of the ova of Lasiocampa fquercus), Saturnia (pavonia) 

 and Bombyx (mori) were independently acquired. It seems just as 

 probable, or even more probable, that Dimorpha branched before, rather 

 than after, the forking of the Lachneid-Saturniid stirps, and possibly 

 very shortly after this stirps had separated from the Sphingid one, having 

 developed independently as regards the reduction in number of tubercles. 



* Larv?e of this species given to me by Dr. Chapman, were, at the time that I 

 received them, too old and specialised to afford much clue to their real position, 

 although both cocoon and pupa suggest primitive Saturniids (Bacot). 



t In the Sphingids all the tubercles are single -haired, except iii on the 

 meso- and metathoracic segments where it bears two hairs ; but judging by the 

 structure of the larvae of such primitive forms as the Hepialids and Zeuzerids, this is 

 in all probability a primitive and not a specialised character (Bacot). 



