Araneida or Spiders 



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 



1. Head of a spider showing 

 poison gland (c) and its re- 



' 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. i), 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- 2 ' 



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 very 

 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. 



