December 1S94.] 



PS re HE. 



173 



among congeneric species, that which 

 deprives us in great part of the advan- 

 tage of indications of comparative 

 anatomy, we can in most cases still 

 recognize the origin as entirely distinct 

 for the two species and establish the 

 resemblance as due to the eflect of the 

 surroundings upon the imago. 



It is this which occiu's, for example, 

 in the case of isotypv- Some related 

 forms such as Picris brassicae and 

 Pieris rafae, the numerous Euplaeae, 

 etc The fact that these species frequent 

 the same localities without mixing and 

 vvitliout crossing indicates that the 

 larval differences wliich they present in 

 the midst of identical conditions are 

 diflerences of ancestry. This is still 

 more evident ^vhe^ it is applied to 

 Hvmenopterous parasites (Isotypes) of 

 which the larvae have the same hosts or 

 of parasites of plants of which the larvae 

 feed side by side upon the same plant. 

 Hormomvia capraeae Bremi is distin- 

 guished with difficulty in the adult state 

 from another Cecidomyian living also 

 verj- often upon the willow (Salix ca- 

 praea). 



The gall has been described by 

 .Schlechtendahl under No. 332.* But 

 the larvae of these two Diptera remain 

 distinct and produce very difterent galls 

 upon the leaves of the same tree. There 

 is here no doubt that the resemblance 

 of the adults is simple convergence and 

 tloes not indicate a closely related 

 ancestry. 



* Schlectendahl, Die Gallbildungen (Zoocecidien) 

 i8gi, p. 40. 



When, in the place of living in the 

 same surroundings the larvae have a 

 diflerent habitat the question becomes 

 more difficult to solve. 



Guenc^'e in a remarkable memoir upon 

 some European bombycesf has con- 

 sidered as distinct species two types, 

 Boiiibyx spartii lib. and Boiiibyx 

 calluiiae Palen, which represent one 

 the southern and the other the northern 

 form of B. querciis L. 



If one examines an extensive collec- 

 tion of B. qiiercus such as that of our 

 colleague M. J. Fallou he will easily 

 see that it is almost impossible to 

 separate the adults of these three 

 species. Certain forms of B. qt/crcus 

 passing manifestly, as Guen^e and 

 Bellier de la Chavignerie already have 

 recognized, in part to B. spartii. in 

 part to B. callunac. 



Gui'nee had discovered that the 

 young caterpillar of B. calhinae differs 

 from that of B . querciis., but that the 

 divergence diminishes after the first 

 moult and finally disappears. One 

 may attempt to see in this dissimilarity 

 of the larvae in the early state a proof 

 of the primitive separation of the two 

 species. But the habitat difl'ers suffi- 

 cienthto explain this divergence. One 

 of the two forms, without doubt B. 

 calliinae., represents the first ancestral 

 larva which is modified in B. qncrcus 

 and B. spartii and this species may 

 truly be considered as a poecilogonic 

 form slightlv modified in the adult 

 stage. 



t Annales Soc. ent. Fr. 1858. 435-442. 



