determine the Cocoon Colour of Plusia moneta. 409 



IV. A reduction of a yellow colour which is at first present. 



Clisiocampa castrensis, Tutt. 



C. neustria, Tutt. 

 This list by no means includes all the British moths which 

 produce occasional white cocoons. 



4. Mendelism and Cocoon Colour. 



Kellogg in America and Toyama and his students in 

 Japan have made a great number of breeding experiments 

 with Bombyx mori, in order to study the inheritance of 

 cocoon colour, but their results are not uniform, apparently 

 because they dealt with different races. No such experi- 

 ments have yet been undertaken with any British moths. 



It is clear from the above observations that in the future 

 all work done on cocoon colour, whether in studying heredity 

 or environment, must take cognisance of the possible effect 

 of moisture. In order to obtain reliable results, all 

 cocoons must have strictly the same environment, not 

 only as regards heat and light, but also as regards moisture. 

 The lack of recognition of the response of cocoon colour to 

 very small differences in moisture, has materially reduced 

 the value of much work already done. 



• • 5. Conclusions. 



1. Except as regards the addition of foreign particles, 

 our knowledge of the causes of the change from white to 

 brown or yellow silk is very superficial, and can only be 

 made complete by a biological and chemical study of silk, 

 both as a dead and a living product. 



2. Even this superficial knowledge has yet to be extended 

 to a considerable number of British species, and some 

 experiments should be repeated, viz. those on Saturnia 

 carpini. 



3. Further investigation will probably co-ordinate the 

 effect upon white silk of intestinal fluids and atmospheric 

 moisture. 



I wish to thank Dr. A. D. Imms, of the Department of 

 Agricultural Entomology of Manchester University, for 

 giving me the opportunity of consulting the scattered 

 literature cited in this paper. 



TRANS. ENT. SOC. LOND. 1916. — PARTS III, IV. (APRIL '17) E E 



