208 THE ENTOMOLOGIST. 



summer, a fact which has never yet been observed. But at the 

 same cool temperature — say, 15° C. — at which the first brood 

 would produce iirorsa butterflies, the second produces exclusively 

 levana butterflies, or at any rate a preponderance of them. 



These facts, as it appears to me, force us to assume, that an 

 alternation of the two forms is provided by nature, apart from the 

 influences of temperature; that in the first brood the prorsa-idi^, 

 in the second, i. e. the first generation of butterflies of the 

 following year, the levana-ids are predisposed to activity, and 

 that they can only be prevented from actual activity by special 

 outward influences. The most important of these influences is 

 the temperature during the pupal period, which acts in such a 

 way that many individuals of the first brood of the year can be 

 induced by cold to assume the levana-, or at any rate the porima-, 

 form, and almost a majority of the individuals of the second 

 brood can be induced by heat to assume the prorsa-form. Appa- 

 rently everything is arranged so that butterflies emerging in the 

 summer possess the jj ?-orsa-f orm, and, indeed, although the summer 

 is not hot, and that all butterflies emerging in the spring possess 

 the levana-ioivQ., although the spring is quite ivarm, as is often the 

 case with us. The experiments have shown, that all hyhernatiiig 

 pupce produce levana witJiout exception, let them be subjected to 

 ever so high a temperature. 



It appears to me that by taking this view of seasonal dimor- 

 phism we obtain a more satisfactory insight into this remarkable 

 phenomenon, than we hitherto possessed. 



(To be continued.) 



SILK-PRODUCING LEPIDOPTERA. 



By Alfred Wailly. 



(Membre Laurcat de la Societe Nationale d'Acclimatation de France). 



(Continued from p. 159.) 



WILD SILKWORMS. 



Asiatic Species. 



Anthertea YAMA-MAi, Gucriu Meneville (Japanese oak silk- 

 worm). This wild silkworm, reared on a large scale in Japan, 

 on account of the beauty and excellent quality of its silk, was 

 introduced into France in 1861, by Guerin Meneville.^ Bred in 

 various parts of Europe with more or less success, it has now 

 almost disappeared, breeders having lost it, or given it up, to 

 rear an easier species, Anthercea pernyi (Chinese oak silkworm) ; 

 but new attempts are being made to rear it again from eggs im- 

 ported from Japan. That which discouraged most breeders was 

 that the eggs generally hatched before the oak buds were suffi- 



