The Sense of Sight in Spiders 285 



The posterior middle eyes in Phidippus are directed consider- 

 ably toward the side and upward. In Lycosa they are directed 

 much more frontward and also upward, while in Heteropoda 

 they look straight upw^ard. Their axes are in this case almost 

 perpendicular to the horizontal plane. 



The posterior side eyes in Phidippus are directed sidewise, 

 considerably upward and a little backward. In Lycosa they are 

 directed in the same way sidewnse and backward but considerably 

 more upward, while in Heteropoda they are directed considerably 

 less upward and much more backward. 



I studied the positions of the eyes as I have described them here, 

 originally in perfectly ripe females. Six individuals of each 

 species were measured and showed only slight differences in the 

 angles. Since the' method employed is not an absolutely exact 

 one, it is difficult to say whether these differences depend upon 

 variation in the position of the eyes or upon defects in the method 

 itself. However, the following facts speak rather for defective 

 measurements than for natural variation. I expected to find 

 that during the post-embryonic development the position of the 

 eyes on the cephalothorax would change with each moulting, 

 approaching more and more nearly to that of the adult female, 

 which should be considered an adaptation to the particular. life 

 of the spider. An observation that made this seem still more 

 probable has been made by various scientists at different times, 

 that the eye-group in young spiderlings occupies a relatively 

 larger part of the cephalothorax than it does in the adult spiders. 

 Nevertheless there seemed to me to be occasion for a more thorough 

 study of the eye-group and the eye-axes in spiders of different 

 ages. I had in my possession perfectly ripe females of the 

 three species I have mentioned, several specimens of Heteropoda 

 just before the final moulting, others that had to moult twice and 

 three specimens of very small spiders that had still to moult at least 

 three times before attaining maturity and also a cocoon filled with 

 very young spiderlings. I kept several females of Lycosa nidicola 

 for a time in large glass jars and preserved both mother and the 

 spiderlings which were in part taken from the cocoon, in part 

 killed while on the back of the mother just as they were about to 



