302 SILK-MOTHS. Chap. VIII. 



by cultivators, and lias not been fixed by selection. Captain Hutton, in 

 the paper before referred to, lias argned with much force that the dark 

 tiger-like marks, which so frequently appear during the later moults in 

 the caterpillars of various breeds, are due to reversion ; for the caterpillars 

 of several allied wild species of Bombyx are marked and coloured in this 

 manner. He separated some caterpillars with the tiger-like marks, and 

 in the succeeding spring (pp. 149, 298) nearly all the caterpillars reared 

 from them were dark-brindled, and the tints became still darker in the 

 third generation. The moths reared from these caterpillars 71 also became 

 darker, and resembled in colouring the wild B. Huttoni, On this view of 

 the tiger-like marks being due to reversion, the persistency with which they 

 are transmitted is intelligible. 



Several years ago Mrs. Whitby took great pains in breeding silkworms 

 on a large scale, and she informed me that some of her caterpillars had dark 

 eyebrows. This is probably the first step in reversion towards the tiger- 

 like marks, and I was curious to know whether so trifling a character would 

 be inherited ; at my request she separated in 1848 twenty of these cater- 

 pillars, and having kept the moths separate, bred from them. Of the many 

 caterpillars thus reared, " every one without exception had eyebrows, some 

 darker and more decidedly marked than the others, but all had [eye- 

 brows more or less plainly visible." Black caterpillars occasionally appear 

 amongst those of the common kind, but in so variable a manner, 

 that according to M. Bobinet the same race will one year exclusively pro- 

 duce white caterpillars, and the next year many black ones ; nevertheless, 

 I have been informed by M. A. Bossi of Geneva, that, if these black cater- 

 pillars are separately bred from, they reproduce the same colour ; but the 

 cocoons and moths reared from them do not present any difference. • 



The caterpillar in Europe ordinarily moults four times before passing 

 into the cocoon stage ; but there are races " a trois mues," and the Trevol- 

 tini race likewise moults only thrice. It might have been thought that so 

 important a physiological difference would not have arisen under domesti- 

 cation ; but M. Bobinet 72 states that, on the one hand, ordinary caterpillars 

 occasionally spin their cocoons after only three moults, and, on the other 

 hand, " presque toutes les races a trois mues, que nous avons experimentees, 

 ont fait quatre mues a la seconde ou a la troisieme annee, ce qui semble 

 prouver qu'il a suffi de les placer dans des conditions favorables pour leur 

 rendre une faculte qu'elles avaient perdue sous des influences moins 

 favorables." 



Cocoons. — The caterpillar in changing into the cocoon loses about 50 per 

 cent, of its weight ; but the amount of loss differs in different breeds, and 

 this is of importance to the cultivator. The cocoon in the different races 

 presents characteristic differences ; being large or small ; — nearly spherical 

 with no constriction, as in the Race de Loriol, or cylindrical with either a 

 deep or slight constriction in the middle ; — with the two ends, or with one 

 end alone, more or less pointed. The silk varies in fineness and quality, 

 and in being nearly white, of two tints, or yellow. Generally the colour of 



71 ' Transact. Ent. Soc.,' nt supra, pp. 153, 308. 72 Bobinet, idem, p. 317. 



