206 Mr. W. Bateson on Vnrintion in the 



coloured cocoon was an abnormal product resulting from 

 unhealthy conditions. 



As regards S. carimii, of the three points given above 

 the second was fully established. No caterpillar which 

 was removed and shut up spun a dark cocoon. The 

 other two points were not fully established, for, while 

 all the cocoons which I could find wild in the hedges 

 were dark, few comparatively of those fed in captivity 

 spun cocoons of full colour. Several of these, however, 

 were attached to white paper, as in (3). 



Lastly, in the case both of Eriogaster and S. carpmi, 

 there was evidence to show a strong probability that the 

 colouring matter was derived from the contents of the 

 alimentary canal, and that in the case of the light 

 cocoons this substance was either evacuated, or not 

 produced, or possibly absorbed. Two points, therefore, 

 remained for further investigation ; first, whether S. 

 carpini, if in healthy circumstances, will spin dark 

 cocoons indejjendently of the colour of its surroundings; 

 and secondly, the far more important question of the 

 nature and origin of the colouring substance. To the 

 solutions of both of these questions the evidence to be 

 given contributes. 



(1). From two batches of eggs I reared about 140 

 larvae of S. carpini. Supposing that my larvae had not 

 been under good conditions last year, I resolved this 

 year to sleeve them on a bush in the open air. On the 

 2nd of July, therefore, when they had made their last 

 moult, I divided them into two lots, A and B. 



A. Sixty-six larvae were placed on a large branch of 

 hawthorn in the Botanic Garden, and were covered with 

 a large sleeve of white muslin. Into this sleeve I put a 

 considerable quantity of crumpled white paper, arranging 

 it so that the paper lay thickly amongst the leaves. In 

 the autumn, when all had spun, I opened the sleeve,' 

 and counted the cocoons, numbering 53, the remainder 

 having presumably escaped. Of these — 



7 were spun on the white sleeve. 



18 were spun in the white paper, or between it and 

 the sleeve. 



19 were spun partially attached to the white paper 

 and partly to twigs, &c. 



9 were spun on leaves or twigs, not attached to the 

 white paper or sleeve. 



