158 Silkworms in India. [ Yo\. I. 



action of some powerful solvent {e.g., caustic potash) to separate the 

 threads. 1 



Both the cement with which the caterpillar hardens the walls of its 

 silken cocoon and also the fluid with which the moth afterwards softens 

 this cement, prior to working its way out. by the help of its wing spines, 

 appears to be secreted in the alimentary tract and to be of excrementi- 

 tious origin. 



"With regard to this cement, Major Coussmaker wrote (February 

 1880):— 



" One of the most interesting and I think important facts that I have this year 

 been able to prove, is -with regard to the composition of the cement with which the 

 caterpillar hardens its cocoon. 



" Former analyses of this agent made for me in England by Dr. Taylor and in 

 Bombay by Dr. Lyon, had shown that it contained the acid urate of ammonia, and it 

 was in fact excrementitious ; and this year, by opening the cocoons at various intervals, 

 I was able to convince myself of the fact that when the caterpillar has left off feeding 

 and begins to spin, it voids the food remaining in the alimentary canal, first of all in a 

 more or less solid form and of a dark colour, but after it has become fully enveloped 

 in the cocoon the excrement comes away as a light-coloured liquid, the hue and con- 

 sistency of which depend upon the amount of vegetable matter not previously evac- 

 uated, and the amount of lime, carbon, and ammonia present. The respective propor- 

 tion of these ingredients vary, I presume, with the food on which the caterpillar has 

 to feed, and with the state of the atmosphere at the time of spinning." — (Wardle.) 



"With regard to the natural solvent of this cement, the observations 

 of the writer seem to show that the solvent fluid, which is stored in a 

 large bladder-like dilatation in the lower portion of the digestive tract of 

 the future moth, can be freely poured out through the anus of the moth 

 into the chrysalis case; but the chrysalis case itself prevents its passing 

 into the lower portion of the cocoon. Now, the moth emerges through 

 a longitudinal dorsal slit in the thoracic segments of the chrysalis, and, 

 in its struggles to extricate itself, it forces this fluid between its body 

 and the chrysalis case through the slit, on to the cemented wall of the 

 cocoon, precisely in the spot where the moisture appears and the soften- 

 ing of the cement takes place prior to the moth's working its way 

 through. It would at first sight appear likely that this excreted fluid, 

 being milk-like in consistency, would, in bathing the abdomen of the 

 moth inside the chrysalis case, stain the delicate scales and hairs with 

 which the moth is covered : that this is not the case, however, is at least 

 indicated by the fact that much of the fluid has been found inside 

 chrysalis cases from which unstained moths have just emerged. 



1 One of the greatest difficulties in reeling tusser silk, after the cocoons have once been 

 softened, is to make the separate strands cohere in the reeled thread ; this difficulty does 

 not occur in the case of mulberry silk where, unlike the tusser, the cement is only softened 

 in the reeling basin, so that on again hardening it serves to glue the strands together. 



