SPIDERS AND MITES 237 



ing the prey, which they powerfully press against the 

 toothed edges of the stout basal piece, by which means 

 the nutritive fluids of the prey are pressed out, and taken 

 into the mouth, when the dried and empty skin is re- 

 jected. The poison is of an acid nature, as experiments 

 performed with irritated spiders prove ; litmus-paper pierced 

 by them becoming red as far around the perforations as 

 the emitted fluid spreads. 



In the slough, the upper surface of the cephalo-thorax 

 is always detached as a thin plate, convex outwardly, con- 

 cave inwardly. As it is upon the front portion of this 

 division of the body that the eyes are situate, the slough 

 displays these with great clearness and beauty beneath the 

 microscope. Here you may see them. The whole slough 

 from its thinness is semi -pellucid, but the eyes transmit 

 the light with brilliance, not, however, as if they were 

 simple round holes, because you can discern very mani- 

 festly a hemispherical glassy coat, by which it is refracted. 



It is, however, when we examine the forehead of a liv- 

 ing or recently killed spider that we see the eyes to advan- 

 tage. In this example of the same species (Clubiona atrox), 

 you see them, like polished globes of diamond, sunk into 

 the solid skin of the head. Their form is unimpeachably 

 perfect, and the reflection of light from their surface most 

 brilliant. 



The arrangement of these lustrous eyes is worthy of at- 

 tention. They are generally eight in number in Spiders, 

 but their relative position varies so much as to afford good 

 characters by which naturalists have grouped them in gen- 

 era. In the Clubiona which we have been examining, they 

 are placed in two nearly straight transverse rows on the 

 forehead; but as this surface is convex, it follows that the 



