45 



V. On Variation in the Colour ot Cocoons of Eriogaster 

 lanestris and Saturnia carpini. By William 

 Bateson, M,A., Fellow of St. John's College, 

 Cambridge. Communicated by Dr. David Sharp, 

 M.A., f!r.S. 



[Read December Siid, 1891.] 



It is well known that the cocoons of certain moths are 

 sometimes dark brown and sometimes of various lighter 

 shades of colour, being occasionally quite white. This 

 variation is well known in the case of the Small Egger 

 {Eriogaster lanestris), and the Emperor Moth {Saturnia 

 carpini). 



It has been suggested by Poulton* and others that 

 these colours are of value as a means of concealment 

 from enemies, and it has been stated by them that the 

 variation in colour of these cocoons accords with that of 

 the substances to which the cocoons are attached. In 

 the place referred to, Poulton says: — "I found that 

 caterpillars of this species {S. carpini) spun very dark 

 brown cocoons in a black calico bag, while white cocoons 

 were spun in white surroundings in a strong light. In 

 this case it seems almost impossible for the surrounding 

 colours to influence directly the colour of the cocoon. 

 It is necessary to assume the existence of a complex 

 nervous circle as a medium through which the stimulus 



of colour can make itself felt The Rev. W. J. 



H. Newman showed that the cocoons of E. lanestris are 

 creamy white when spun on white paper, dark brown 



when constructed among leaves The fact that 



light reflected from green leaves is here the stimulus for 

 the production of a dark colour is readily intelHgible 

 when we remember that the moth does not emerge till 

 the following February at the earliest, while the insect 

 often remains in the pupal state for one or two years 

 longer. The leaves in contact with the cocoon soon die 



* E. B. Poulton, « Colours of Animals,' 1890, pp. 142—146. 

 TRANS. ENT. SOC. LOND. 1892. — PART I. (MARCH.) 



