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 in 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 0, which appears 
to be along a little shallow groove in the Fic, 242. Much magnified outline of the falx 
outer surface of the inside face of the nd fang of Argiope cophinaria. g.m., matrix 
5 . of the poison gland; en, canal which contains 
fangs. The outlet (0) is shown again at the duct leading from the gland; 0, opening 
x, magnified about thirty times. The  onthesideofthe fang; tt, theteeth; ot, dotted 
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. 
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 
Fic. 248. 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. 
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