{_Ancistrodon_ {North America, Florida, { { Texas, Mexico, Guatemala. { {_Lachesis_ {Central and South America, { { Martinique, St. Lucia. { { VIPERIDÆ _Crotalinæ_ {_Sistrurus_ {North America east of the { { Rocky Mountains, Mexico. { { { {Southern Canada, British { { Columbia, Central America, {_Crotalus_ { Guiana, Venezuela, { { Brazil, Uruguay, Northern { { Argentina. PART II. CHAPTER IV. _SECRETION AND COLLECTION OF VENOM IN SNAKES._ _Non-poisonous_ 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 indispensable 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 demonstration of 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 Bertrand, 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, we 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 enormous dimensions. They may attain the size of a large almond (_Crotalus_, _Naja_), and they then occupy the spacious chamber already described (Chap. I., p. 10), which is situated behind the eye on each side of the skull.