408 Mrs. Onera A. Merritt Hawkes on the Factors which 



the brown colour. Dewitz and Bateson are in agreement 

 as to an intestinal liquid producing the brown colour, but 

 Bateson does not state that he distinguished between a 

 first and a second ejection. Peligot, in one of the earliest 

 papers on Bombyx mori, writes that the frass is first deposited, 

 and sometime later a drop of clear alkaline liquid con- 

 taining bicarbonate of potassium, and then " it (the larva) 

 moves away and finds a place in which to spin." The 

 second deposit in Bombyx differed from that of S. carpini 

 in that it is deposited before the cocoon is spun, in which 

 case it is difficult to see how it can have any subsequent 

 influence on the silk. 



Dewitz repudiates the statement of Levrat and Conte, 

 that an intestinal fluid colours white silk by means of a 

 foreign matter added to the outside of the silk fibres. 



Dr. A. D. Imms kindly sent me two white cocoons of 

 Clisiocampa neustria, which became yellow when placed in 

 a damp box. 



3. Results of the above Expeeiments. 



So few attempts have been made to discover the ulti- 

 mate cause of changes in cocoon colour, that the subject 

 is almost untouched ground. The causes suggested for 

 producing white cocoons may, pro temp., be tabulated as 

 follows. Each division is followed by the names of the 

 moths of which we have any knowledge and the name of 

 the observer. 



I. The absence of an intestinal fluid (*. e. either an 



excretion from the intestine, or the secretion of the 

 Malphigian tubules). 



Saturnia carpini, Dewitz. 



Poecilocampa populi, Tutt. 



Hemaris fuciformis, Tutt. 



Leucoma salicis, Tutt. 



Eriogaster lanestris, Bateson. 



II. A comparatively dry environment. 



Plusia moneta. Merritt Hawkes. 



Halias prasinana, Poulton (see p. 406 above). 



Clisiocampa neustria, Merritt Hawkes. 



III. A lack of foreign particles which are normally woven 

 into the cocoon. 



Hemerophila abruptaria, Poulton. 

 Chelonia caia, Tutt. 



