CHAPTER XVI.
1.—INVERTEBRATES.
Besides reptiles, many other animals possess poison-glands and inoculatory organs which they employ, either to defend themselves against their natural enemies, or to capture the living prey upon which they feed.
The venoms that they produce are still, for the most part, but little understood. A few of them, however, have excited the curiosity of physiologists, especially those secreted by certain batrachians, such as the Toad, and certain fishes, such as the Weever. Some of them exhibit close affinity to snake-venom, and are composed, like the latter, of proteic substances modifiable by heat and precipitable by alcohol; others possess altogether special characters, and resemble alkaloids.
The lowest animal group in which these secretions begin to be clearly differentiated is that of the Coelenterates.