EFFECT OF MOISTURE UPON SILK OF HYBRIDS 53 



the leaf never being large enough to extend entirely around the 

 cocoon. 



The second generation of cocoons (F2) varied much more than 

 Fi some being a dark red, the majority fawn, and a few so light 

 in colour that one was inclined to describe them as white. These 

 very light cocoons, however, were found, when opened, to have 

 a fawn coloured lining, whereas those of P. ricini which I had 

 reared myself, were white throughout. Ali the nets used in 

 rearing this generation were black. 



Mr. W. Bateson very kindly looked at the cocoons of the Fx 

 and Fo generations, and, influenced by his own early work on 

 cocoon colour, advised a very careful study of every possible 

 environmental influence. As a result, hours were spent in watch- 

 ing the larvae spin. It was thus ascertained amongst other 

 facts, that the first silk produced might be either brown or white. 

 I was, however, never successful in collecting this first silk 

 straight from the mouth of the larvae, but have seen sufficient 

 on the glass lid of a cell, to have no doubt of the colour. The 

 brown silk, even w^hen thus seen in some quantity, was a fawn 

 brown, never the deep red-brown which characterised so many 

 completed cocoons. 



Bateson had worked at Eriogaster lanestris and Saturnia 

 carpini and concluded that they spun a very light or white cocoon 

 as a result of unhealthy conditions or "unnatural conditions such 

 as disturbance at the time of spinning or removal from the food 

 plant when the growth is nearly complete." That unhealthy 

 conditions had nothing to do with the light cocoons produced 

 in this hybrid is, I think, quite clear from the general condition 

 of the larvae as described above. Mr. J. H. Watson, a well 

 known breeder, inspected the larvae and stated that he had never 

 seen any in better condition. Disturbance, in the case of this 

 hybrid had no influence, as is demonstrated by the experiments 

 presently to be described. 



Whilst these general observations were in progress, a number 

 of larvae were being reared, for special breeding pm-poses, in 

 separate cells. In every case except one, these larvae produced 

 deep brown cocoons. These cells, being filled with privet leaves, 



