20 4 THE POPULAR SCIENCE MONTHLY. 



necting the hind-limbs with the rest of the skeleton. The pelvic arch 

 is thus almost universally present, but of the limb proper there is, as 

 far as is yet known, not a vestige in any of the large group of toothed 

 whales, not even in the great Cachalot or sperm whale, although it 

 should be mentioned that it has never been looked for in that animal 

 with any sort of care. With regard to the whalebone whales, at 

 least to some of the species, the case is different. In these animals 

 there are found, attached to the outer and lower side of the pelvic 

 bone, other elements, bony or only cartilaginous as the case may be, 

 clearly representing rudiments of the first and in some cases the sec- 

 ond segment of the limb, the thigh or femur, and the leg or tibia. 



"VYe have here a case in which it is not difficult to answer the ques- 

 tion before alluded to, often asked with regard to 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 framework which strengthens it and 

 perfects its functions. It would be impossible, on any theory of causa- 

 tion yet known, to conceive of a limb gradually developed from within 

 outward. On the other hand, its disappearance would naturally take 

 place in the opposite direction. 



We turn next to what the researches of paleontology teach of the 

 past history of the order. Unfortunately, this does not at present 

 amount to very much. We know nothing of their condition, if they 

 existed, in the Mesozoic age. Even in the cretaceous seas not a frag- 

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

 Cetaceans, of whose organization 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 be- 

 tween that of the existing sub-orders of whales. In fact, Zeuglodon is 

 precisely what we might have expected a priori an ancestral form of 

 whales to have been. From the middle Miocene period fossil Cetacea 

 are abundant, and distinctly divided into the two groups now existing. 

 The Mystacocetes, or whalebone whales, of the Miocene seas, were, as 

 far as we know now, only Balmnopterw, some of which were more gen- 

 eralized than any now existing. In the shape of the mandible also, 

 Van Beneden discerns some approximation to the Odontocetes. Right 

 whales (Halcena) have not been found earlier than the Pliocene period, 

 and it is interesting to note that, instead of the individuals diminishing 

 in balk as we approach the times we live in, as with many other groups 

 of animals, the contrary has been the case, no known extinct species 



