172 



PSrCHE. 



[December 1S94. 



the problem, we may hope that a more 

 complete knowledge, that is a knowl- 

 edge of the dynamic embryology of 

 a large number of species, will give 

 us the solution. 



At present we may distinguish two 

 principal categories of insects which 

 are similar in adult stages and difler in 

 earlier stages of development. 



First : certain insects pertaining to 

 the same genus or to distinct genera, 

 sometimes even widely separated, 

 which present in all cases larval stages 

 which are quite different and in each 

 case adult forms similar b}' conver- 

 gence, a convergence due to the sur- 

 rounding conditions (protective resem- 

 blance, mimicry direct and indirect, 

 isotypy, etc.). 



Second : ;miong other insects the 

 different generations of the same spe- 

 cies considered at different points of 

 their geographical distribution, at dif- 

 ferent seasons of the year, or in different 

 conditions of nutrition, have larvae 

 which are dissimilar while the adults 

 are very similar to each other antl 

 present very slight modifications. It 

 is to this form that we apply the term 

 Poecilogony.* In this case the larvae 

 have become divergent in adapting 

 themselves to different ethological sur- 

 roundings. The final result is the 



*A. Giard, Sur le bourgeonnement des larves 

 d'Astellium spongiforme Gd. et sur la poecilogonie 

 Chez les ascidies composees (C. R. de I'Academie 

 des Sciences, 2 Fevrier 1891). 



A. Giard, Nouvelles remarques sur la poecilo- 

 gonie (C. R. de I'Academie des Sciences, 27 Juin 

 1891). 



same in all cases but from the point 

 of view of consanguinity and therefore 

 of natural classification the two cate- 

 gories are far from having the same 

 signification. 



The related species of poecilogonie 

 origin iiave between them direct parent- 

 age and approach each other notwith- 

 standing their einbivonic divergencies. 

 The species which resemble each other 

 by convergence can on the contrary 

 have only phylogenic separation and 

 must be considered as naturally distinct. 

 From a practical point of view it is not 

 always easy to decide if two simil;ir 

 forms are poecilogenic or convergent 

 species. In certain cases, however, the 

 distinction is easy and no doubt is per- 

 missable. When, for example, the 

 species which by selection have become 

 convergent, belong to genera sufficiently 

 separated, the profound anatomic char- 

 acters and the embryonic characters are 

 not altered by convergence to the point 

 of being unrecognizable. The resem- 

 blance is only superficial and if the older 

 naturalists have been deceived b}' a 

 similar aspect of the adults the error is 

 not possible to-day. Mimicry, so perfect 

 in Leptalis and Ithomia, of Papilio 

 paradoxa and Euplaea midatnns ; 

 imitation of Danaides or of the Acraeides 

 by different species of Papilio or of 

 Diadema do not impose upon any en- 

 tomologist. 



The resemblance although less exact 

 in other respects of Dichonia aprilina 

 and JMoma orioii is, nevertheless, an 

 example of the same kind. Even when 

 convergence of the adults takes place 



