The Sense of Sight in Spiders 



299 



the retina to a boat or canoe in some eyes and to a deep bag in 

 others. This may be ascertained not only from sections. It is 

 sometimes possible to remove the entire retina intact from the vitre- 

 ous body whose proximal end fills it out and to examine it in toto 

 under the microscope. The vitreous body also varies in shape 

 in different eyes and is usually considerably elongated in the 

 direction of the eye-axis in those eyes which form the largest 

 images. The vitreous body is especially long in the anterior 

 middle eyes of jumping spiders, Phidippus tripunctatus, for 

 example, and is shaped something like a long cone with its base 

 which is concave, toward the lens, its axis being at the same time 

 the axis of a conical hole which extends through its entire length. 

 This hole also is largest at the lens and much smaller lat the 

 retina and may be seen in sagittal and cross-sections. It is also 

 sometimes visible in young spiderlings of the jumpers, where it 

 presents a likeness to a pupilla. In life it is probably filled out 

 with a liquid. 



Roughly speaking the size of the image is in direct proportion 

 to the size of the eye but measurements show discrepancies which 

 must be due to differences in the curvatures of the lenses. The 

 following table illustrates this. 



TABLE IX 



Ratios of diameters of eyes and of images to the diameter of the AME and its image. Compa'e with 



Fig. 10 



AME 



ASE 



PME 



PSE 



/eye 



1 image 



/eye 



1 image 



Lycosa nidicola I 



1 image 



Phidippus tripunctatus 

 Heteropoda venatoria. . 



This table shows that while there is a dependence of the size 

 of the image upon the size of the eye, this dependence is not of 

 such a kind as to allow of definite conclusions in regard to the 

 smallest angle of vision from measurements of the eyes and 



