All the Cetacea are predaceous, subsisting on living animal food of some kind. One genus alone (_Orca_) eats other warm-blooded animals, as Seals, and even members of its own order, both large and small. Some feed on fish, others on small floating crustaceans, pteropods, and medusæ, while the principal staple of the food of many is constituted by the various species of cephalopods, _Loligo_ and other _Teuthidæ_, which must abound in certain seas in vast numbers, as they form almost the entire support of some of the largest members of the order. In size the Cetacea vary much, some of the smaller Dolphins scarcely exceeding 4 feet in length, while others are the most colossal of all animals. It is true that most statements of their bulk found in general and even zoological literature are greatly exaggerated, but even when reduced to their actual dimensions (which will be stated under the respective genera) some of the existing Whales exceed in size any animal living either at present or in former times of which we have any certain evidence. With some exceptions, the Cetacea generally are timid inoffensive animals, active in their movements, and very affectionate in their disposition towards one another, especially the mother towards the young, of which there is usually but one, or at most two at a time. They are generally gregarious, swimming in herds or “schools” (so termed by the whalers) sometimes amounting to many thousands in number; though some species have hitherto only been met with either singly or in pairs.