WHALES AND THEIR NEIGHBORS. 249 



common with the giraffe, the elongation of whose neck is produced 

 not by introduction of new vertebra?, but by the great development 

 of the normal number, seven. The manatees, however, present a very 

 remarkable exception to this most general of rules, in that they pos- 

 sess only six vertebrae in their necks. The only other exceptions to the 

 rule of seven, as the normal number of neck-vertebra? in quadrupeds, 

 are found in one species of sloth which has six vertebra? like the mana- 

 tee, and in another kind of sloth which possesses nine. Then, also, 

 the manatees possess a heart of very curious conformation, its apex or 

 tip being widely cleft or divided a feature much more plainly marked 

 in these animals than in the elephants and seals, whose hearts, anatomi- 

 cally speaking, are also divided. The manatees possess well-developed 

 molars or grinding teeth, but have no front teeth in the adult state. 

 Like the whalebone whale, however,- the young manatee bas front 

 teeth, these again disappearing before birth, and presenting us once 

 more with examples of rudimentary organs which possess a reference 

 " to a former state of things." 



What evidence is at hand respecting the remote ancestors of the 

 whales and their neighbors ? is a question which may form a fitting 

 conclusion to these brief details of the family history of the group. 

 The geological evidence shows us that the whales are comparatively 

 "recent" forms, speaking geologically, and dealing notwithstanding 

 the word " recent " with very remote and immense periods of time. 

 Among the oldest fossil whales we find one form in particular (Zeug- 

 lodon) which had teeth of larger kind than are possessed by any 

 living whale, this creature being by some authorities regarded as link- 

 ing the whales with the seals. The fossil remains of Zcuglodon and 

 its neighbors first occur in Eocene rocks that is, in the oldest forma- 

 tions of the Tertiary series, and in rocks of relatively " recent " nature. 

 These remarkable creatures were as gigantic as their living representa- 

 tives. One species is known to have attained a length of seventy feet. 

 Their remains are of such frequent occurrence in the " Jackson Beds " 

 of the United States, that Professor Dana remarks: "The large ver- 

 tebra?, some of them a foot and a half long and a foot in diameter, 

 were formerly so abundant over the country in Alabama, that they 

 were used for making walls, or were burned to rid the fields of them." 

 The teeth of this curious monster of the vasty Eocene deep were of 

 two kinds, and included front teeth of conical shape, and grinders or 

 molars ; the latter exhibiting a striking peculiarity in that they were 

 formed each of two halves, or teeth united by their crowns, but sepa- 

 rated at their roots. Zeuglodon appears to connect the whales and 

 their neighbors with the seals and walruses, and thus in one sense may 

 be said to constitute, if not a " missing link," at least an intermediate 

 form of anomalous kind, when viewed relatively to the existing ceta- 

 ceans. According to the geological evideuce at hand, we may assume 

 that the modifications which have produced the existing whales and 



