THE EFFECT OF MOISTURE UPON THE SILK OF 



THE HYBRID PHILOSAMIA (ATTACUS) RICINI 



BOISD. c^ X PHILOSAMIA CYNTHIA 



(DRURY) 9 



ONERA A. MERRITT HAWKES 



Philosamia ricini and of P. cynthia from Ning-po were crossed 

 in 1914 in order to study the method of inheritance of certain 

 spots on the larva, the colour of the cocoons, and the ar- 

 rangement of the long white hairs on the abdomen of the moth. 

 The results of the preliminary work on cocoon colour are given 

 in this paper, no reference being made to the still unfinished work 

 on the larva and moth. 



When the cocoon colour work was undertaken, it was hoped 

 that the results would help to explain the lack of coincidence be- 

 tween the work of Kellogg and Toyama on the inheritance of 

 colour in cocoons. The breeding, thus far, has thrown no light 

 upon the method of inheritance, but, if the cocoons used by them, 

 are as much affected by moisture as the hybrid here discussed, 

 their results may have to be considerably modified. 



Philosamia ricini is found wild in Assam, but has also been 

 domesticated to a considerable extent in that province, and to a 

 smaller degree, in other parts of India. A careful study of the 

 life history has been made at Pusa, India. The form there culti- 

 vated is not pure, some larvae being spotted instead of spotless, 

 and some of the cocoons being a pale fawn instead of a pure white. 

 Every effort is, however, made to keep the broods as nearly as 

 possible like the wild form, which has a spotless larva and a pure 

 white cocoon. Owing to the uncertainty of the Pusa stock, the 

 specimen used in this cross was chosen from a batch of white 

 cocoons collected in the Assam forests. 



In order that there should be no doubt about the stock, Mr. J. 

 H. Watson and myself, mated males and females of this batch 



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