This family of Whales is again susceptible of division into the two sub-families--Physeterinae or Sperm Whales and the Ziphiinae or Beaked Whales. Professor P. J. van Beneden was strongly against any subdivision of what is here regarded as a perfectly natural family, embracing the Physeters and the Beaked Whales. There are, however, some reasons for the subdivision. The Ziphiinae have a reduced series of teeth, never exceeding two on each mandible, which contrasts with the fully-toothed mandibles of both _Physeter_ and _Kogia_. The stomach of the Ziphioids is extraordinarily complicated even for a Cetacean. The small head of the latter group, which recalls in a curious way that of Mosasauroid reptiles and some Dinosaurs, is in contrast to the {363} enormous head of the Cachalot and the very fairly-developed skull of the "Pygmy Sperm Whale." Both, however, furnish spermaceti, and in various osteological details come near together. On the whole we incline towards separating the Cachalots from the Ziphioids, and shall therefore commence with the former as being in some respects the more primitive members of the family Physeteridae. SUB-FAM. 1. PHYSETERINAE.--This sub-family may be thus defined:--Teeth in lower jaw numerous. No distinct lachrymal bone. Stomach with only four compartments (? as to _Kogia_). Of this sub-family the best-known genus is _Physeter_, including the Sperm Whale or Cachalot. Of other reputed species we shall speak later. The genus is characterised in the first place by its large size--as much as 82 feet of length have been assigned to _Physeter macrocephalus_; but Sir William Flower thought that 55 or possibly 60 feet might be a better approximation to the greatest length of the Cachalot. The head is enormous, a third of the length of the body, and terminates in a massive and bluntish snout. This is, however, not so abruptly truncated as is often represented in figures. According to Messrs. Pouchet and Chaves,[246] it slopes forward two metres beyond the end of the lower jaw; the mouth is thus ventral and almost shark-like in position, as is the case also with the Pygmy Sperm Whale, to be considered later. In connexion with this peculiar position of the mouth, it has been asserted--Mr. F. T. Bullen figures it[247]--that the Sperm Whale turns over upon its back to bite. The blow-hole is single, and shaped like the sound-hole of a violin; it lies upon one side, and is not median in position. The throat is grooved as in the Ziphioids by two grooves. The dorsal fin is represented by a whole series of lowish humps, decreasing in elevation from before backwards. The pectoral fins are not large relatively speaking. The great square head is not occupied entirely by the skull; the cavity lying above, which is of course traversed by the tube ending in the blow-hole, is filled with the spermaceti, which is fluid fat during the life of the animal. Spermaceti also occurs in other Whales;