October 2, 1893.] 



KNOWLEDGE. 



185 



ficial or epithelial layer. The whole of this stupendous 

 horny growth takes place, however, after birth, young 

 whales having smooth palates, with no trace of the horny 

 plates. Although at birth young whalebone whales show 

 no traces of the substance from which the group derives 

 its name, they equally exhibit no evidence of the 

 presence of teeth. If, however, their jaws be examined at 

 a still earlier stage of development, it will be found that 

 there are a number of small teeth lying within a groove 

 beneath the gum on each side of both the upper and the 

 lower jaws. Previous to birth these teeth become absorbed, 

 and thus never cut the gum. Their presence in this 

 transitory stage is, however, of the deepest interest to 

 the evolutionist, since they unmistakably indicate the 

 derivation of the whalebone whales from ancestors 

 provided with a full series of functional teeth. This, 

 however, is not the whole of the story these rudi- 

 mentary structures have to tell. From the recent 

 investigations of Dr. Kiikenthal, it appears that in addition 

 to the above-mentioned tooth-germs, the jaws of very 

 young whales likewise exhibit traces of a still earlier 

 deciduous series of milk-teeth ; thus showing that the 

 former correspond to the permanent series of other 

 mammals. Accordingly, these tooth-germs do not represent 

 the functional teeth of the toothed whales, which, as we 

 have seen in the article on that group, correspond to the 

 milk-teeth of ordinary mammals. Even more remarkable 

 are certain observations relating to the structure of these 

 tooth-germs. It has been shown, indeed, that the teeth in 

 the latter part of the series, when first formed, consist of a 

 number of adjacent cusps, and that as development 

 proceeds these cusps become completely separated from 

 each other so as to constitute distinct individual teeth of 

 a simple conical form. 



This discovery is of the very highest import, since it 

 serves to indicate how the numerous simple conical teeth 

 of the dolphins and other toothed whales have probably 

 been derived by the splitting and subdivision of originally 

 complex cusped teeth more or less closely resembling 

 those of the extinct zeuglodonts referred to in our article 

 in the last number. 



Being primarily distinguished from the toothed whales 

 by their total absence of teeth after birth and the presence 

 of whalebone in the adult condition, the whalebone whales 

 present certain other distinctive characters to which we 

 may now brieHy allude. 



In the first place, the whales of this gi'oup differ 

 externally from all those furnished with teeth in that their 

 nostrils open externally by two distinct longitudinal slit- 

 like apertures ; while, if we cut into the head, we shall find 

 that there is a distinct organ of smell, of which all traces 

 have disappeared among the toothed whales. Moreover, 

 instead of the skull being invariably unsymmetrical in the 

 region of the nose, as it is in the latter group, it retains 

 the normal symmetry ; while, instead of the mere nodules 

 which in the toothed whales represent the nasals of other 

 mammals, in the whalebone whales these bones are fairly 

 well developed. Moreover, the lower jaw of any member 

 of the present group may always be distinguished from 

 that of a toothed whale not only by the absence of teeth, 

 but likewise by the circumstance that each of its branches 

 is much bowed outwards in the middle, while their anterior 

 extremities are connected together only by ligamentous 

 tissue, instead of by a bony symphysis of greater or lesser 

 length. Many other points of difference between the two 

 groups might be cited, but we have especially referred to 

 those mentioned above, for the reason that while the 

 presence of whalebone indicates that in one respect the 

 members of this group are more specialized than their 



toothed cousins, in regard to the structure of the skull in 

 the region of the nose and the retention of an organ of 

 smell, as well as in the double apertures of the nostrils, 

 they depart less widely from the ordinary mammalian 

 type. And it is from this evidence that zoologists regard 

 the two main groups of whales as being widely divergent 

 branches from a common ancestral stock, if, indeed, they 

 do not go so far as to consider that each has had a totally 

 independent origin. 



With regard to the number of forms by which they are 

 represented, the whalebone whales are far less numerous 

 than the toothed group, while the whole of them are 

 included within a single family. What the group lacks in 

 number is, however, amply made up by the great bodily 

 size of its various representatives. Among the toothed 

 whales, the sperm-whale alone attains gigantic dimensions ; 

 whereas in the present group there are several species, 

 such as the Greenland whale, which nearly equal that 

 enormous creature in bulk, while two of the rorquals far 

 surpass it. This, however, is by no means all, for whereas 

 the great majority of the dolphins and porpoises are 

 relatively small cetaceans of less than twenty feet in 

 length, the smallest member of the present group is the 

 New Zealand pigmy whale, which attains a length of 

 twenty feet, while next to this comes the lesser rorqual, 

 whose length is frequently close on thirty feet. 



Of the various genera of this group, the most specialized 

 are the typical or right whales (linUma), in which the 

 black whalebone is far larger and more elastic than in any 

 of the others, except the pigmy whale ; while, in order to 

 accommodate it in the mouth, the skull has the 

 palate narrower and much more highly arched, and 

 the two branches of the lower jaw more outwardly 

 bowed than in the other members of the group. Ex- 

 ternally, these whales — which are commercially of far 

 greater value than the undermentioned rorquals — are 

 characterized by the inordinately large dimensions of the 

 head, by the smooth thi-oat, the moderate length of the 

 flippers, and the total want of a back-fin. So gigantic, 

 indeed, is the size of the mouth in these whales that its 

 capacity actually exceeds that of the whole of the other 

 cavities of the body ; and yet the size of the throat is so 

 small as almost to justify the common nautical saying that 

 a herring will choke a whale. There are but two well- 

 defined species of right whales, viz., the Greenland or 

 Arctic whale {B. iiiystirctus), and the southern right 

 whale (B. (iii.stralis), the latter of which was nearly 

 exterminated some centuries ago in tlie Atlantic by the 

 Basque whalers, while the former is only too likely to share 

 the same fate at the hands of their modern successors in 

 the Arctic seas. Of the two, the Greenland whale is 

 decidedly the more specialized, having a much larger head 

 and longer whalebone, and is in this respect facile pruiccjis 

 among its tribe ; although, as it only measures from forty- 

 five to fifty feet in length, it is inferior in point of size to 

 the rorquals. The skeletons of both these whales are cha- 

 racterized by the whole of the vertebrae of the neck being 

 welded together into a solid mass ; and the same feature 

 is exhibited by that of the pigmy whale [Neohalana) of the 

 Australasian seas, which, as already mentioned, is a mere 

 dwarf among giants, as it does not exceed some twenty feet 

 in total length. Agreeing also with the right whales in 

 its smooth throat, the pigmy whale differs by having a 

 small hook-like fin on the back, while its long and elastic 

 whalebone is white instead of black. Far larger than 

 the last, the great grey whale of the Pacific (Rhachianectes) 

 forms a kind of connecting link between the right whales 

 and the rorquals, having the smooth throat and finless 

 back of the former, while its whalebone is even shorter 



