174 



PSrCHE. 



[December 1894. 



We have elsewhere direct proof of 

 tlie existence of poecilogony among 

 insects. In two very important memoirs 

 pubHshed in Russian and of whicli we 

 have a translation by our learned 

 colleague C. R. von Osten Sacken, the 

 Russian entomologist Portchinsky has 

 demonstrated that the common Musca 

 corvina presents two distinct forms in 

 different parts of its wide habitat. In 

 the north of Russia this coprophagous 

 fly generally deposits 34 eggs of medium 

 size from which arise larvae that present 

 two very distinct phases of evolution. 

 In the Crimea where coprophagous 

 insects are more abundant and con- 

 sequently the struggle for life more 

 intense, the same Dipteron deposits 

 only one large egg in which the 

 metamorphosis is very rapid and con- 

 densed and recalls that of the Pupipara, 

 the larva arriving almost immediately 

 at its last phase of development. 

 Analogous cases are known among 

 different Lepidoptera and notably in 

 the mulberry silk-worms {Sericaria 

 mori). In the south of Europe this 

 species furnishes an interesting race 

 called Trevolttni which not only pro- 

 duces several generations annually but 

 is distinguished from the type in that 

 the caterpillars have only three moults 

 in place of four. Cultivated in the 

 north this race regains the ordinary 

 characters of the species (the sec- 

 ond or third year) as shown by Robi- 

 net.* 



As the caterpillar of Sericaria mori 



*Robinet, Art d'Slever les vers a sole ; traduction 

 du conite Dandolo, 1825, p. 317. 



varies more or less the physiological 

 peculiarity of the suppression of one 

 moult attracts the eye, but in other 

 cases structural modifications are more 

 apparent. 



Th. Goossens has indicated several 

 very interesting examples of geographic 

 poecilogony. Deilephila eufhorbiae 

 does not present in Ardache and in 

 Var the ordinary yellow points and the 

 rosy spots are replaced by spots of a 

 pale yellow. The caterpillar of Helio- 

 this marginata, light or green in the 

 North is more often of an almost black 

 brown in Provence. Iia the south of 

 France the dorsal part of the caterpillar 

 of Zygaena fausta is almost always' 

 tawny. At Paris this part is water 

 green. f 



When in cases of this kind the adults 

 of two poecilogonic varieties come to 

 differ but little at the two extremities of 

 its habitat, we do not err if we establish 

 two species, saying : Without doubt 

 the perfect insects differ but little, but 

 the larvae present differences so great 

 as not to permit us to unite the two 

 forms. This is certainly what occurs 

 for a large number of species called 

 representative for the old and the new 

 world, Triaena psi and T. occiden- 

 talism for example. Comparison of the 

 monographs of Gu^ni^e an(.l Abbot is 

 very instructive in this respect. 



Sometimes even the variation of the 

 adults rests exclusively upon the ana- 

 tomical characters of the genital 

 apparatus of such a kind that the 



tTh. Goossens, Des variations sur les ctienilles 

 (.Ann. See. ent. Fr., 1871, p. 118). 



