384 HISTOLOGY 



bony spine (sp.) and that the poison cells are developments of the clavate 

 cells which were carried in with this epithelium. In fact, the one kind 

 can be continuously traced into the other in Figure 349, A. 



Such tissues are also found in many other bony fishes. The " weavers " 

 and their allies have them, and in Thalassophryne, a marine form, they 

 are developed to formidable proportions. 



FIG. 349. A, tip of a fin-spine of the river catfish, Schilbeodes; B, section through the body 

 wall to include the auxiliary poison gland and the base of the pectoral spine of this fish. 

 ep., epidermis with clavate cells (c.c.) ; p.g., invaginated epidermis with clavate cells modified 

 to become poison cells; sp., spine; pg., pigment cells; /., fat cells. Both clavate and poison 

 cells have double nuclei. (After H. D. REED.) 



Passing by the amphibians, whose so-called poison glands are used 

 mostly to produce offensive odors, we find that the reptiles have the 

 best-developed venomous organs. In the rattlesnake, Crotalis horridus, 

 a beautifully developed tooth is transformed into a fang by the presence 

 of a groove on its anterior surface. This groove is turned into a tube by 

 the overlapping of its edges, leaving an upper and a lower aperture. 



Above, in the connective tissue on the side of the jaw, an invaginated 

 region of the integument forms a large gland with many irregular, al- 

 veolar lobules each of which is lined with a simple cuboidal epithelium 

 (Fig. 350, A, B). The cells have a large, somewhat flattened nucleus 



