238 



EVENINGS AT THE MICEOSCOPE. 



FANG OF SPIDEE. 



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 rejected. 

 The poison is of an acid 

 nature, as experiments 

 performed with irritated 

 spiders prove; litmus-pa- 

 per pierced by them be- 

 coming 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 out- 

 wardly, concave 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 manifestly a hemispherical glassy 

 coat, by which it is refracted. 



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

 living or recently killed spider, that we see the eyes to 

 advantage. In this example of the same species {Olub- 

 iona atrox), you see them, like polished globes of dia- 

 mond, 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 

 attention. They are generally eight in number in 

 Spiders, but their relative position varies so much, as to 



