318 SILK-MOTHS. Chap. VIIL 



hatch until the following spring ; and it is in vain, says M. Eobinet, 

 to expose them to a temperature gradually raised, in order that the 

 caterpillar may be quickly developed. Yet occasionally, without 

 any known cause, batches of eggs are produced, which immediately 

 begin to undergo the proper changes, and are hatched in from 

 twenty to thirty days. From these and some other analogous facts 

 it may be concluded that the Trevoltini silkworms of Italy, of which 

 the caterpillars are hatched in from fifteen to twenty days, do not 

 necessarily form, as has been maintained, a distinct species. 

 Although the breeds which live in temperate countries produce 

 eggs which cannot be immediately hatched by artificial heat, yet 

 when they are removed to and reared in a hot country they 

 gradually acquire the character of quick development, as in the 

 Trevoltini races. 71 



Caterpillars. — These vary greatly in size and colour. The skin 

 is generally white, sometimes mottled with black or grey, and 

 occasionally quite black. The colour, however, as M. Eobinet 

 asserts, is not constant, even in perfectly pure breeds ; except in 

 the race tigree, so called from being marked with transverse black 

 stripes. As the general colour of the caterpillar is not correlated 

 with that of the silk, 72 this character is disregarded by cultivators, 

 and has not been fixed by selection. Captain Hutton, in the paper 

 before referred to, has argued 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 73 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 



71 Robinet, ibid., pp. 12, 318. I would ultimately have been acquired, 



may add that the eggs of N. American See review in 'Athenaeum,' 1844-, p. 



silkworms taken to the Sandwich 329, of J. Jarves' 'Scenes in the 



Islands produced moths at very irre- Sandwich Islands.' 



gular periods ; and the moths thus 72 ' The Art of rearing Silk-worms,' 



raised yielded eggs which were even translated from Count Dandolo, 1825, 



worse in this respect. Some were p. 23. 



hatched in ten days, and others not 73 'Transact. Ent. Soc.,' ut supra, 



until after the lapse of many months. pp. 153, 308. 

 No doubt a regular early character 



