226 WHALES y PAST AND PRESENT xv 



rudimentary parts, Are they disappearing or are they incipient 

 organs ? We can have no hesitation in saying that they are 

 the former. All we know of the origin of limbs shows that 

 they commence as outgrowths upon the surface of the body, 

 and that the first-formed portions are the most distal segments. 

 The limb, as proved by its permanent state in the lowest 

 Vertebrates, and by its embryological condition in higher 

 forms, is at first a mere projection or outward fold of the skin, 

 which, in the course of development, as it becomes of use in 

 moving or supporting the animal, acquires the internal frame- 

 work which strengthens it and perfects its functions. It 

 would be impossible, on any theory of causation yet known, to 

 conceive of a limb gradually developed from within outwards. 

 On the other hand, its disappearance would naturally take 

 place in the opposite direction ; projecting parts which had 

 become useless, being in the way, would, like all the other 

 prominences on the surface of the whales, hair, ears, etc., be 

 removed, while the most internal, offering far less interference 

 with successful carrying on the purposes of life, would be the 

 last to disappear, lingering, as in the case of the Greenland 

 whale, long enough to reveal their wonderful history to the 

 anatomist who has been fortunate enough to possess the skill 

 and the insight to interpret it. 



Time will not allow of more illustrations drawn from the 

 structure of existing Cetacea; we turn next to what the 

 researches of palaeontology teach of the past history of the 

 order. Unfortunately this does not at present amount to very 

 much. As is the case with nearly all other orders of 

 mammals, we know nothing of their condition, if they existed, 

 in the mesozoic age. Even in the Cretaceous seas, the deposits 

 at the bottom of which are so well adapted to preserve the 

 remains of the creatures which swam in them, not a fragment 

 of any whale or whale -like animal has been found. The 

 earliest Cetaceans of whose organisation we have any good 

 evidence are the Zeuglodons of the Eocene formations of 

 North America. These were creatures whose structure, as 

 far as we know it, was intermediate between that of the 

 existing sub-orders of whales, having the elongated nasal bones 

 and anterior position of the nostrils of the Mystacocetes, with 



