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



of light. H. W. Andrews found that cocoons on Larkspur 

 were yellow, whilst those on Monkshood were white. 



6. Bowles mentions that the cocoon, if spun indoors, is 

 white, if out of doors, bright yellow. 



The impression that white cocoons, such as the above, 

 produce poor imagines, may be due to the deterioration of 

 the pupa, if there is a continuance of the dry conditions 

 under which such cocoons were spun. It is known by all 

 breeders that the environmental condition during the 

 pupal stage is a factor of great importance, and that 

 very subtle differences in warmth and moisture may cause 

 non-emergence or cripples. It is frequently more difficult 

 to get the right environment for the pupa than for the 

 larva. Crampton states, in reference to Philosamia cynthia 

 (advena) : " The perfect imagines constituted only 16*6% of 

 the whole number of individuals which entered the cocoons, 

 from which we may gain an idea of the severity of the 

 conditions under which the quiescent pupa exists." 



2. Experiments by various Observers upon White 

 Cocoons of other Species. 



Prof. E. B. Poulton has made extensive experiments 

 with larvae which produce cocoons of various colours, and 

 believes that in the majority of experiments white or 

 pale cocoons were produced as a protective device by the 

 larvae. If the white surroundings to which he refers 

 (A) means white paper, which is dry when compared with 

 green leaves, the whiteness may have been due to dryness. 



One of his own experiments confirms my observations 

 concerning the importance of a damp environment. On 

 p. 450 (C) he relates that he put two larvae of Halias 

 prasinana in two chip boxes (presumably dry), and both 

 spun white cocoons. The first specimen, after having 

 spun-up, was removed from its cocoon — in the process, 

 it was cut and also found to be attacked by an ichneumon. 

 It was then placed among oak leaves (comparatively 

 damp), and there spun a brown cocoon. The second 

 specimen was also removed from its cocoon, and placed in 

 rolls of black net (presumably dry), where it began a second 

 white cocoon. The second part of this experiment should 

 be repeated, the black or any other coloured net being 

 slightly damped. 



Bateson in criticising the work of Poulton says, p. 205 : 



