EYES OF THE SPIDER. 289 



Now, taking for example the eyes of a Spider, it would be 

 natural to suppose that the same result would occur, especially 

 as the foci of the eyes point in different directions. The left- 

 hand figure in the illustration represents the eight eyes of one 

 of our common Spiders, belonging to the genus Clubiona, which 

 may be found in almost any outhouse, sitting in its curious web, 

 and ready in a moment to run for safety into its silken tunnel. 



It will be seen that the foci of all the eyes are in different 

 directions, and so placed as to command a large radius. Ob- 

 servers have remarked that the eyes are placed in Spiders so as 

 to suit their habits. " Those spiders," writes Professor Owen, 

 in his " Comparative Anatomy,'' " which hide in tubes, or lurk 

 in obscure retreats, either underground or in the holes or fissures 

 of wails or rocks, from which they emerge only to seize a passing 

 prey, have their eyes aggregated in a close group in the middle 

 of the forehead, as in the Bird-spider, the Clotho, &c. 



"The spiders which inhabit short tubes, terminated by a 

 large web, exposed to the open air, have the eyes separated and 

 more spread upon the front of the cephalothorax. 



" Those spiders which rest in the centre of a free web, along 

 which they frequently traverse, have the eyes supported on 

 slight prominences, which permit a greater divergence of their 

 axis ; this structure is well remarked in the genus Thomka, the 

 species of which live in ambuscade in flowers. 



"Lastly, the spiders called Err antes, or Wanderers, have 

 their eyes still more scattered, the lateral ones being placed at 

 the margin of the cephalothorax.' ' 



Yet, although each eye produces a separate image, it is clear 

 that upon the mind of the Spider only a single idea can be 

 impressed, for that otherwise all would be confusion. There 

 must, therefore, be some mechanism in the structure of the eye, 

 the nature of which we are not as yet able to understand. 



A still more remarkable instance of a natural Multiplying- 

 glass may be found in the eyes of many insects. 



The form of multiplying- glass shown in the accompanying illus- 

 tration is probably familiar to most of my readers. It consists of 

 a convex piece of glass, cut into a number of facets, and showing 

 in each facet a distinct and separate image of the object to 

 which it is directed. Now, the compound eves of insects are 



