172 PROCEEDINGS OF THE ACADEMY OF [1888. 



May 15. 



Rev. H. C. McCook, D. D., Vice-President, in the chair. 



Eighteen persons present. 



The deaths were announced of Caleb Cope, a member, on the 

 12th, inst. and Dr. Gerhard Vom Rath, a correspondent, April 23. 



A paper entitled " Notes on new species of Orb-weaving Spiders." 

 By Rev. Henry C. McCook was presented for publication. 



Notes on the Relations of Structure and Function to Color 

 'Changes in Spiders. — Rev. Dr. Henry C. McCook submitted the 

 following remarks on color changes in spiders, which he Avished to 

 be understood as in jiart, at least, tentative. They were intended to 

 evoke suggestions and helpful information from members of the 

 Academy and others, rather than to present final conclusions on a 

 most interesting subject. 

 I. On the Relation of Structure to Color he observed that : — 



1 The color of young spiders is almost without exception light 

 yellow, or green, whitish or livid, tints that blend very well with the 

 prevailing greens of foliage, young twigs and the grays of bark of 

 trees, of rocks and soil. This is due largely to the fact that the tis- 

 sues are at that time translucent, allowing a free play of light through 

 them. The effect is also, probably, caused by the absence of food in 

 the alimentary tract and lack of distribution of nutriment throughout 

 the system. 



As young spiders advance in age the color deepens, which is 

 caused no doubt by gradual hardening of the tissues, thus making 

 them more opaque. Up to this period no food has been taken, hence 

 the absence of food alone is not sufficient to account for the light 

 colors of the first stages after exode. Yellows and browns in vari- 

 ous tints occur at this period, and in some cases, not generally he 

 believed, color patterns which are characteristic of the various spe- 

 cies in adult life begin to appear with more or less distinctness, or 

 at least suggestively. It is not until sedentary spiderlings have es- 

 tablished themselves upon their own webs, and so to speak, have set 

 up housekeeping for themselves, that the characteristic colors of the 

 species begin to appear with any positive degi-ee of distinctness. 



2 As the spide];s further advance in age and make their success- 

 ive moults, various color changes may be noted. Immediately after 

 moulting the color is always lighter, which is probably due to the 

 fact that the harder skin, just cast off, jireveuted the passage of light 

 through the tissues. The new skin is probably thinner, and more 

 translucent. Dr. McCook believed that moulting produces changes 

 in color patterns of a very decided kind, at least in certain species. 

 Apparently some organic change occurs which is the cause of this 

 phenomenon. 



