206 EVENINGS AT THE MICROSCOPE. 



joint are permeated by a slender membranous tube, which 

 is the poison duct, and which terminates at the open 

 extremity of the former, while at the other end it commu- 

 nicates with a lengthened oval sac where the venom is 

 secreted. This, of course, we do not see here, for it is 

 not sloughed with the exuviae, but retained in the interior 

 of the body; but in life it is a sac, extending into the 

 cephalo-thorax, as that part of the body which carries 

 the legs is called, and covered with spiral folds pro- 

 duced by the arrangement of the fibres of its contractile 

 tissue. 



When the Spider attacks a fly, it plunges into its 

 victim the two fangs, the action of which is downwards, 

 and not from right to left, like that of the jaws of insects. 

 At the same instant a drop of poison is secreted in each 

 gland, which, oozing through the duct, escapes from the 



perforated end of the 

 fang into the wound, and 

 rapidly produces death. 

 The fangs are then clasped 

 down, carrying the prey, 

 which they powerfully 

 press against the toothed 

 FANG OF SPIDER. edges of the stout basal 



piece, by which means the nutritive fluids of the prey are 

 pressed out, and taken into the mouth, the dried and 

 empty skin being rejected. The poison is of an acid 

 nature, as experiments performed with irritated spiders 

 prove ; litmus paper pierced by them becoming red as far 

 round 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 



