20G 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 

 communicates 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 exuvise, 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 

 produced by the arrangement of the fibres of its con- 

 tractile tissue. 



When the Spider attacks a fly, it plunges into its 

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

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

 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 clasp- 

 ed down, carrying the 

 prey, which they power- 

 fully press against the 



FANG OP SPIDER. j.1 1 1 p j 1 



toothed edges or 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 



