Chap. VIII. THEIE DIFFEKENCES. 303 



the silk is not strictly inherited : bnt in the chapter on Selection I shall 

 give a cnrious account how, in the course of sixty-five generations, the 

 number of yellow cocoons in one breed has been reduced in France from 

 one hundred to thirty-five in the thousand. According to Robinet, the 

 white race, called Sina, by careful selection during the last seventy-five 

 years, " est arrivee a un tel etat de purete, qu'on ne voit pas un seul cocon 

 , jaune dans des millions de cocons blancs." 73 Cocoons are sometimes formed 

 as is well known, entirely destitute of silk, which yet produce moths ; un- 

 fortunately Mrs. Whitby was prevented by an accident from ascertaining 

 whether this character would prove hereditary. 



Adult stage.— I can find no account of any constant difference in the 

 moths of the most distinct races. Mrs. Whitby assured me that there was 

 none in the several kinds bred by her; and I have received a similar 

 statement from the eminent naturalist M. de Quatrefages. Captain Hutton 

 also says H that the moths of all kinds vary much in colour, but in nearly the 

 same inconstant manner. Considering how much the cocoons in the several 

 races differ, this fact is of interest, and may probably be accounted for on 

 the same principle as the fluctuating variability of colour in the cater- 

 pillar, namely, that there has been no motive for selecting and perpetuating 

 any particular variation. 



The males of the wild Bombycidse "fly swiftly in the day-time and 

 evening, but the females are usually very sluggish and inactive." 5 " 5 In 

 several moths of this family the females have abortive wings, but no 

 instance is known of the males being incapable of flight, for in this case the 

 species could hardly have been perpetuated. In the silk-moth both sexes 

 have imperfect, crumpled wings, and are incapable of flight; but still 

 there is a trace of the characteristic difference in the two sexes; for 

 though, on comparing a number of males and females, I could detect 

 no difference in the development of their wings, yet I was assured by 

 Mrs. Whitby that the males of the moths bred by her used their wings 

 more than the females, and could flutter downwards, though never up- 

 wards. She also states that, when the females first emerge from the 

 cocoon, their wings are less expanded than those of the male. The degree 

 of imperfection, however, in the wings varies much in different races and 

 under different circumstances ; M. Quatrefages ^ says that he has seen a 

 number of moths with their wings reduced to a third, fourth, or tenth 

 part of their normal dimensions, and even to mere short straight stumps : 

 " ll me semble qu'il y a la un veritable arret de developpement partiel." 

 On the other hand, he describes the female moths of the Andre Jean breed 

 as having « leurs ailes larges et etalees. Un seul presente quelques cour- 

 , , bures irreguheres et des plis anomaux." As moths and butterflies of all 



lands reared from wild caterpillars under confinement often have crippled 

 wings, the same cause, whatever it may be, has probably acted on silk- 



« ^^t id T;P^ 31 I- ~H^T^ansact. Ent. SoC idem, 



Transact. Ent. Soc.,' ut supra, p. 152. 



Y) Q1 H met " 



; 5 (j, ,, mo , T11 , .. iTr 76 ' Etudes sur les Maladies du Ver 



'* Stephens Illustrations, ' Haus- a Soie ' 1859 ™ wx 900 

 tellala/ vol. ii. p. 35. See also Capt. ' ' PP< 3 ° 4 ' 2 ° 9 " 



