VIII THE COLOURS OF SPIDERS 183 



name to Epeira trifolium. The relative uniformity 

 of the cephalothorax is perhaps in part associated 

 with the uniform thickness of its cuticle. The mark- 

 ings of the abdomen are, as we shall see later in more 

 detail, probably associated with the tendency of the 

 epidermal pigment to become aggregated round the 

 little pits which indicate the points of attachment of 

 the muscles. M'Cook . considers that the variation 

 in colour and markings which is so marked in the 

 abdomens of many spiders, may be due in part to 

 variations in the amount of distention in this region 

 due to the presence of eggs and so on. 



Dr. M'Cook's volumes contain many other interest- 

 ing observations on the relations of colour to habitat 

 in spiders, on instances of so-called mimicry, etc., for 

 which reference must be made to the original. There 

 are various observations in the literature of the subject 

 tending to prove that spiders in some instances can 

 vary their tints according to their environment ; that 

 harmony with the colours of the environment which 

 is known as " protective coloration " seems also to be 

 relatively common. 



