147 



PART 11. 



CHAPTER IV. 



SECRETION AND COLLECTION OF VENOM IN 



SNAKES. 



Non-poisonouH as well as poisonous snakes possess parotid and 

 upper labial glands capable of secreting venom. In the former the 

 organs of inoculation are wanting, but we shall see later on that 

 the toxic secretion of their glands is just as mdispensable to them 

 as to the snakes of the second category for the purpose of enabling 

 them to digest their prey. 



For the morphological, histological, and physiological demon- 

 stration ot the existence of these glands in harmless reptiles we 

 are indebted to Leydig (1873), whose discovery has since been 

 confirmed and extended by the researches of Phisalix and Ber- 

 trand, Alcock, L. Rogers, and L. Lannoy. 



The parotids of Grass Snakes are mixed glands of the sero- 

 mucous type. The serous tubes are situate almost exclusively in 

 the posterior portion of the gland. As we proceed towards the 

 anterior portion, w^e find that these serous tubes are interspersed 

 with others which are exclusively mucous or sero-mucous, and they 

 become entangled with those of the upper labial gland, properly 

 so-called. The substance of the gland is divided into several lobes 

 by bands of connective tissue ; the tubes are separated by septa of 

 the same tissue, in extremely delicate layers (Lannoy). 



In poisonous snakes these glands are much more developed, 

 especially in their hinder portions, which sometimes assume 



