ON THE SICNSOK'Y PIT OF THE CROTALIN^. 57 



the outer surface of the membraue. These processes pass 

 between the cells of the supporting layer, and connect the 

 outer flattened nerve-cells with the inner branched nerve- 

 cells, the latter being in direct continuity with the nerve- 

 fibres (cf. PL 4, fig. IG). 



III. Conclusion. 



That this large and prominently situated sense-organ of 

 the pit viper must be of some considerable use to the animal 

 there can be no doubt, but no likely suggestion has been 

 made concerning its probable function. Russell and Horae,^ 

 so long ago as 1804, expressed the idea that the apparatus 

 was a " membrana nicfcitans," but at that time the sensory 

 nature of the organ had not been discovered. Demoulins ^ 

 (1854) writes, " organes particulieres, dont I'usage on la 

 fonction ne sont pas connus; " and Boulenger^ (1890) states 

 that ''the physiological significance of this pit is still 

 unknown." 



It is reasonable to suppose that an organ of this nature 

 must be concerned with some peculiarity in the mode of life 

 of the crotaline snakes, but no recorded observations offer 

 the slightest clue to the presence of anything aberrant in the 

 habits of these animals not exhibited by other vipers. 



The thin wall separating the organ from, the orbit and the 

 groove leading from the pit to the eye are somewhat remark- 

 able features, and may be of more significance than is at first 

 sight apparent. Again, the main partition stretched across 

 the hollow of the maxillary bone like the membrane of a 

 drum is an interesting feature, especially as it is the only 

 truly sensory part of the organ. 



Another feature exclusively possessed by the Crotalinee 

 among venomous snakes is the sphincter near the termina- 

 tion of the poison duct, and, as the sense-organ is lodged 



' Russell and Home, I. c. (1804). 



' Demoulins: cf. Bibronu. Demeril's'Erpetologie,' 1854 (videLeydig, 1. c). 



3 Poulenger, ' Fauna of Brit. India : llept. and Batracli.,' 1890, p. 418. 



