EFFECT OF MOISTURE UPON SILK OF HYBRIDS 57 



pheric conditions are of paramount importance in determining 

 the ultimate colour of the cocoons. The experiments, however, 

 throw no light upon the innate difference between the white silk 

 of the hybrid which becomes brown in a moist atmosphere and 

 the white silk of the parent Philosamia ricini, which remains 

 white under all variations of atmospheric moisture. 



When two cocoons are formed, one white and one brown, side 

 by side on the net, during the same night, there is some differ- 

 ence in the condition of the two which is difficult to explain by 

 the slight difference in atmospheric moisture which would occur 

 in a small, closed room, between 10 p.m. and 8 a.m. There is 

 here, doubtless, a difference in inheritance, such that the one pos- 

 sessed and the other did not, the power to produce brown silk 

 at the particular temperature and degree of moisture, which 

 occurred in that room and on that night. Nevertheless, all the 

 white or hght cocoons made thus, side by side with brown ones, 

 became, even after four months, brown when exposed to a very 

 moist atmosphere. It is a matter of regret that the conditions 

 under which the experiments were made, did not admit of con- 

 stant observations with a wet and dry bulb thermometer. 



But, although atmospheric moisture can change white silk to 

 brown, there remains the possibility, that cocoon colour is nor- 

 mally affected by an excretion. 



The larvae, just before beginning to spin, pass a large evacua- 

 tion which consists of the ordinary frass in a drop of greenish 

 liquid. When dry, this liquid becomes a deeper green. Obser- 

 vations were made five or six times a day, to ascertain whether 

 the cocoons were wet or even damp, as if soaked by an excretion, 

 but such were never found, the cocoons were invariably dry. 

 The colour of the cocoons was frequently irregular, thus the body 

 of the cocoon might be a medium brown, but the peduncle, by 

 which it was attached to the branch or \sdre, might be almost 

 colourless. This condition suggested that an excretion might 

 have reached to the end of the cocoon, but did not extend as far 

 as the peduncle. The constant dryness of the cocoons, however, 

 appears to negative this possibility. The irregularity of the 

 colour was possibly due to the looser arrangement of the silk on 



