Juiy 5. 1883] 



NA TURE 



229 



Of the structure of the pelvis and hind limb we are at 

 present in ignorance. 



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 

 Bala>noptera, isome of which (as the genus Cetotheriunt) 

 were, in the elongated flattened form of the nasal bones, 

 the greater distance between the occipital and frontal 

 bone at the top of the head, and the greater length of the 

 cervical vertebra?, more generalised than any now existing. 

 In the shape of the mandible also, Van Beneden, to whose 

 researches we are chiefly indebted for a knowledge of these 

 forms, discerns some approximation to the Odontocetes. 

 Right Whales (Balcena) have not been found earlier than 

 the Pliocene period, and it is interesting to note that instead 

 of the individuals diminishing in bulk 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 

 of whales equalling in size those that are now to be met 

 with in the ocean. The size of whales, as of all other 

 things whose most striking attribute is magnitude, has 

 been greatly exaggerated ; but when reduced to the limits 

 of sober fact, the Greenland Right Whale of 50 feet long, 

 the Sperm Whale of 60, and the Great Northern Rorqual 

 {Balanoptera Sibbaldii) of 80, exceed all other organic 

 structures known, past or present. Instead of living in 

 an age of degeneracy of physical growth, we are in an 

 age of giants, but it may be at the end of that age. For 

 countless ages impulses from within and the forces of 

 circumstances from without have been gradually shaping 

 the whales into their present wonderful form and gigantic 

 size, but the very perfection of their structure and their 

 magnitude combined, the rich supply of oil protecting 

 their internal parts from cold, the beautiful apparatus of 

 whalebone by which their nutrition is provided for, have 

 been fatal gifts, which, under the sudden revolution pro- 

 duced on the surface of the globe by the development of 

 the wants and arts of civilised man, cannot but lead in a 

 few years to their extinction. 



It does not need much foresight to divine the future 

 history of whales, but let us return to the question with 

 which we started, What was their probable origin ? 



In the first place, the evidence is absolutely conclusive 

 that they were not originally aquatic in habit, but are 

 derived from terrestrial mammals of fairly high organisa- 

 tion, belonging to the placental division of the class, — 

 animals in which a hairy covering was developed, and 

 with sense organs, especially that of smell, adapted for 

 living on land ; animals, moreover, with four completely- 

 developed pairs of limbs on the type of the higher verte- 

 brata, and not of that of fishes. Although their teeth are 

 now of the simple homodont and diphyodont type, there 

 is much evidence to show that this has taken place by the 

 process of degradation from a more perfect type, even the 

 roetal teeth of Whalebone Whales showing signs of differ- 

 entiation into molars and incisors, and many extinct 

 forms, not only the Zeuglodons, but also true dolphins, as 

 the Squalodons, having a distinct heterodont dentition, the 

 loss of which, though technically called a "degradation," 

 has been a change in conformity to the habits and needs 

 of the individuals. So much may be considered very 

 nearly if not quite within the range of demonstrated 

 facts, but it is in determining the particular group of 

 mammals from which the Cetacea arose that greater diffi- 

 culties are met with. 



One of the methods by which aland mammal may have 

 been changed into an aquatic one is clearly shown in the 

 stages which still survive among the Carnivora. The 

 seals are obviously modifications of the land Carnivora, 

 the Otaria, or Sea-Lions and Sea-Bears, being curiously 

 intermediate. Many naturalists have been tempted to 

 think that the whales represent a still further stage of the 

 same kind of modification. So firmly has this idea taken 



root that in most popular works on zoology in which an 

 attempt is made to trace the pedigree of existing mammals, 

 the Cetacea are definitely placed as offshoots of the 

 Pinnipedia, which in their turn are derived from the 

 Carnivora. But there is to my mind a fatal objection 

 to this view. The seal of course has much in common 

 with the whale, inasmuch as it is a mammal adapted 

 for an aquatic life, but it has been converted to its 

 general fishlike form by the peculiar development of 

 its hind-limbs into instruments of propulsion through 

 the water ; for though the thighs and legs are small, the 

 feet are large and are the special organs of locomotion in 

 the water, the tail being quite rudimentary. The two feet 

 applied together form an organ very like the tail of a fish or 

 whale, and functionlly representing it, but only functionally, 

 for the time has I trust quite gone by when the Cetacea 

 were defined as animals with the "hinder limbs united, 

 forming a forked horizontal tail." In the whales, as we 

 have seen, the hind-limbs are aborted and the tail deve- 

 loped into a powerful swimming organ. Now it is very 

 difficult to suppose that, when the hind-limbs had once 

 become so well adapted to a function so essential to the 

 welfare of the anim il as that of swimming, they could ever 

 have become reduced and their action transferred to the 

 tail ; — the animal must have been in a too helpless condi- 

 tion to maintain its existence during the transference, 

 if it took place, as we must suppose, gradually. It is far 

 more reasonable to suppose that whales were derived 

 from animals with large tails, which were used in 

 swimming, eventually with such effect that the hind-limbs 

 became no longer necessary, and so gradually disap- 

 peared. The powerful tail, with lateral cutaneous flanges, 

 of an American species of Otter {Pteronura sandbachii) 

 or the still more familiar tail of the beaver, may give 

 some idea of this member in the primitive Cetacea. I 

 think that this consideration disposes of the principal 

 argument that the whales are related to the seals, as most 

 of the other resemblances, such as those in the characters 

 of their teeth, are evidently analogous resemblances 

 related to similarity of habit. 



As pointed out long ago by Hunter, there are numerous 

 points in the structure of the visceral organs of the 

 Cetacea far more resembling those of the Ungulata than 

 the Carnivora. These are the complex stomach, simple 

 liver, respiratory organs, and especially the reproductive 

 organs and structures relating to the development of the 

 young. Even the skull of Zeuglodon, which has been 

 cited as presenting a great resemblance to that of a seal, 

 has quite as much likeness to one of the primitive pig- 

 like Ungulates, except in the purely-adaptive character 

 of the form of the teeth. 



Though there is, perhaps, generally more error than truth 

 in popular ideas on natural history, I cannot help think- 

 ing that some insight has been shown in the common 

 names attached to one of the most familiar of Cetaceans 

 by those whose opportunities of knowing its nature have 

 been greatest — "Sea-Hog,"' "Sea-Pig," or "Herring- 

 Hog" of our fishermen, Meerschwein of the Germans, 

 corrupted into the French " Marsouin," and also " Porc- 

 poisson," shortened into " Porpoise." 



A difficulty that might be suggested in the derivation 

 of the Cetacea from the Ungulata, arising from the latter 

 being at the present day mainly vegetable feeders, is not 

 great, as the primitive Ungulates were probably omni- 

 vorous, as their least modified descendants, the pigs, are 

 still ; and the aquatic branch might easily have gradually 

 lecome more and more piscivorous, as we know from the 

 structure of their bones and teeth, the purely terrestrial 

 members have become by degrees more exclusively 

 graminivorous. 



One other consideration may remove some of the diffi- 

 culties that may arise in contemplating the transition of 

 land mammals into whales. The Gangetic Dolphin 

 (Platanista) and the somewhat related Inia of South 



