236 EVENINGS AT THE MICROSCOPE 



grooves. This whole organ falls into the furrow of the 

 basal joint, when not in use, exactly as the blade of a 

 clasp-knife shuts into the haft; but when the animal is 

 -excited, either to defend itself or to attack its prey, the 

 fang becomes stiffly erected. 



By turning the object on its axis, and examining the 

 extreme tip of the fang, we see that it is not brought to a 

 fine point, but that it has the appearance of having been 

 cut off slantwise just at the tip; and that it is tubular. 

 Now this is a provision for the speedy infliction of death 

 upon the victim; for both the fang and the thick basal 

 joint are permeated by a slender membranous tube, which 

 is the poison duct, and which terminates at the open ex- 

 tremity 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, 

 L extending into the cephalo- 

 thorax as that part of the 

 body which carries the legs is 

 PANG OF SPIDEB. called and covered with spi- 



ral folds produced 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 downward, 

 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, carry- 



