EFFECTS AND USES OF SPIDER POISON. 



269 



The gland itself was well observed in a dissection made from Epeira 

 domiciliorum, and represented at Fig. 243, multiplied about twenty-five times. 

 The sac is covered with muscular fibre, as shown hi the drawing, and yet 

 more magnified in the camera lucida sketch of a portion of the sac 

 at Fig. 244. This muscular provision 

 implies a formidable arrangement for 

 expressing the contents of the gland 

 through the duct and its canal out of 

 the opening in the fang, o. 



Still another view is given at Fig. 

 245, the poison apparatus of Epeira di- 

 ademata. The sac or poison gland, g, is 

 inclosed in its coating of striated mus- 

 cles; the duct, d, about the length of the 

 gland, enters the falx and fang, f, and 

 the outlet is shown at o, which appears 

 to be along a little shallow groove in the FlG 242- Much magnified outline of the 



OUter Surface Of the inside face Of the and fan S of Argiope cophinaria. g.m., matrix 



fangs. The outlet (o) is shown again at 



x, magnified about thirty times. The 



muscular fibres coil spirally and very 



regularly around the bag. The aperture is not only an oval slit, but the 



side towards the point is doubly beveled, thus facilitating the emission and 



direction of the venom. 1 



As the discharge of the poison is not dependent upon the mechanical 

 action of erecting the fang, as in the case of poisonous snakes, it is not 

 improbable that the spider has the power of withholding the poison at 

 will. As the emission of the venom depends on the compression of the 

 muscles by the poison sac, and this compression is within the volition 



of the poison gland ; en, canal which contains 

 the duct leading from the gland; o, opening 

 on the side of the fang ; tt, the teeth ; ot, dotted 

 outline of the outer row. 



FIG. 243. View of the muscular system inclosing the poison gland of Epeira domiciliorum. 

 Camera lucida sketch. X 25. 



of the spider, we may well suppose that the animal often strikes without 

 feeling the necessity of injecting poison into the wound, but destroys its 

 prey simply by piercing. That this arrangement is general among the 

 tribes of spiders appears by a similar examination of any other indi- 

 vidual. 



1 From " Science Gossip," December, 1867, page 270, Mr. Henry Davis. 



