50 Mr. W, Bateson on variation in the colour 



but I found it difficult to obtain any considerable number 

 of dark cocoons from carjjini larvae in captivity, even when 

 they were left with their food, and disturbed as little as 

 possible. 



Fifteen larvae, which were shut up in various dark 

 substances, such as brown paper, black muslin, green 

 muslin, &c., spun cocoons which were all light in colour, 

 though attached to dark substances, several being quite 

 white. No dark cocoon was spun by any larva thus 

 confined. 



Fifteen larvae were fed in a large vessel on food sur- 

 rounded with crumpled white paper, treated as the 

 Erior/aster larvae were in experiment V. Of these 15, 

 only 7 spun dark cocoons ; but of these, 3 were more or 

 less attached to white paper, the remaining 4 being 

 among leaves. 



4 were light brown in colour, being attached to both 



twigs and paper. 

 4 were white or nearly so, being attached to paper 



and leaves. 



From this it seems to be difficult to get conditions which 

 are sufficiently healthy to enable the larvae to spin dark 

 cocoons, but it does not appear that the colour of the 

 cocoons depends upon that of foreign substances. 



Most of the bags and vessels in which the larvas were 

 confined were found to be bespa'tered with brown fluid 

 similar to that which was seen in the case of the Erio- 

 gaster. 



The colouring substance of the cocoons. — It has been 

 mentioned that many of the larvse of Eriogaster and of 

 Saturnia evacuated a quantity of brown fluid substance. 

 The tint of this fluid so closely matches that of the 

 brown cocoons that it seems possible that their colour 

 may be given to them by an outpouring of the brown 

 fluid upon them. In view of this possibility the nature 

 of this fluid is a matter of interest, and the following 

 facts relathig to it have a bearing on the question of the 

 coloration of cocoons. 



The brown fluid was found only in vessels in which 

 large and presumably full-fed larvae were living. In 

 cases in which a larva was removed and shut up, it was 

 generally present on the second or third day after 

 removal, but there were several large patches of it in the 



