Araneida or Spiders 
7 
Head of a spider showing 
poison gland ( c ) and its re¬ 
lation to the chelicera (a). 
the presence of definite and well-developed poison glands can easily 
be shown. They occur as a pair of pouches (fig. i) lying within the 
cephalothorax and connected by a delicate 
duct with a pore on the claw of the chelicera, 
or so-called “mandible” on the convex surface 
of the claw in such a position that it is not 
plugged and closed by the flesh of the victim. 
The glands may be demonstrated by slowly 
and carefully twisting off a chelicera and 
pushing aside the stumps of muscles at its 
base. By exercising care, the chitinous wall 
of the chelicera and its claw may be broken 
away and the duct traced from the gland to its outlet. The inner 
lining of the sac is constituted by a highly developed glandular 
epithelium, supported by a basement membrane of connective 
tissue and covered by a muscular layer, (fig. 2). The muscles, which 
are striated, are spirally arranged (fig. 1), and are doubtless under 
control of the spider, so that the amount of poison to be injected into 
a wound may be varied. 
The poison itself, according to Kobert (1901), is a clear, colorless 
fluid, of oily consistency, acid reaction, and very bitter taste. After 
the spider has bitten two or three times, its supply is exhausted and 
therefore, as in the case of snakes, the poison of the bite decreases 
quickly with use, until it is null. To what extent the content of the 
poison sacs may contain blood serum or, at least, active principles of 
serum, in addition to a specific poison formed by the poison glands 
themselves, Kobert regards as an open question. He believes that 
the acid part of the poison, if really present, 
is formed by the glands and that, 
in the case of some spiders, the 
ferment-like, or better, active 
toxine, comes from the blood. 
But there is a wide difference 
between a poison which may kill 
an insect and one which is harm¬ 
ful to men. Certain it is that 
there is no lack of popular belief 
and newspaper records of fatal 
cases, but the evidence regarding the possibility of fatal or even vein- 
serious results for man is most contradictory. For some years, 
we have attempted to trace the more circumstantial newspaper 
3. Chelicera of 
spider. 
Section through a venom 
gland of Latrodectus 
13 -guttatus showing 
the peritoneal, muscu¬ 
lar and epithelial layers. 
After Bordas. 
