The Sense of Sight in Spiders 305 



arising from possible variations hereditarily fixed through several 

 generations. I scarcely need to add that several mothers and many 

 young ones of the same species were examined. 



The distance between the centers of the rods in all eves of the 

 spiderling is smaller than the corresponding distance in the eves 

 of the adult. Thus in the PME of an adult Lvcosa nidicola the 

 distance between the rods in the center of the retina was found to 

 be 8u while the corresponding distance in the PME of the young 

 is only 2.5/i. The diameters of these eves are respectively 689,^ 

 and 148'!. Or the proportion between the diameters is f^ = 

 4.65, while the proportion between the rods is only = 3.2. ^^ ith 

 other words, the image of the same object will cover a smaller 

 number of rods in the eve of the spiderling than in that of the 

 adult, say 6 X 6 = 36 rods in the former and 9 X 9 = 81 rods 

 in the latter. The same proportion holds for all eves of Lvcosa 

 but when I compared the images in the eyes of this adult female 

 with those of her voung ones that had been allowed to remain on 

 her back for several days longer and were beginning to leave her. 

 I found that this ratio already falls to 4 : 3.5 and becomes i : i 

 after the next moulting. Pardosa nigropalpis showed the same 

 conditions and we should expect the same to be true of other 

 spiders, too. 



CONCLUSIONS 



In drawing conclusions from the facts described, I am well 

 aware that the methods employed in this research are far from 

 perfect. It is possible that the angles of the eve-axes will with 

 time be measured more exactly, that the figures given for the 

 maximal angles of vision will be a little altered in the one or the 

 other sense, that the minimal angle or limit of vision will be found 

 to be one minute larger or smaller, but in one respect the method 

 employed gives facts that cannot be disputed; I mean that the 

 error, whether large or small, is the same for the entire series of 

 the same kind, so that the relation or ratio will remain unchanged. 

 We cannot be sure that the maximum angle of vision in the AME 

 of Phidippus is exactly 40° or that its smallest angle of vision is 

 precisely 8', but we mav be sure that the largereves of an individual 



