September 1, 180:T. 



NOWLEDGE 



161 



(^ 



\^ AN ILLUSTRATED "^^ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: SEPTEMBER 1, 1893. 



CONTENTS. 



PAGE 



Toothed Whales and their Ancestry. By R. Ltdekkee, 



E.A.Cautab 161 



Galls and their Occupants —TIT. By E. A. BiJ tt.er ... 164 



The Light-Changes of Y Cygni. V.y Miss A. M. Clerke 166 



The Great Lunar Crater Copernicus. By A. C. R.iN'v.iRD 169 



Science Notes 17l' 



Letters:— J. R. Holt: H. St. A. Alder ; W. T. Ltnx; 



E. F. Macgeorge : E. W. MArxnER; A. M. C'ierke 



173 



The Face of the Sky for September. By Hebbbet 



Sadlee, F.R.A.S 178 



Chess Column. By 0. D. Locock, B.A.Oxon. 



179 



TOOTHED WHALES AND THEIR ANCESTRY. 



By E. Lydekkee, B.A.Cantab. 



WITHIN the entire limits of tbe great mammalian 

 class, there are, perhaps, no creatures which 

 arouse a larger amount of interest — both 

 among the general public and among natu- 

 ralists — than those included under the names 

 of whales, dolphins and porpoises, and collectively known 

 as cetaceans. One reason for this universal interest is, 

 doubtless, that among these denizens of the deep 

 are comprised the largest animals, not only of 

 the present day, but likewise, so far as our 

 information allows us to speak, of all epochs. 

 Then, again, the fact that such apparently fish- 

 hke creatures are really warm-blooded mammals, 

 suckling their young in the manner distinctive 

 of other members of the class, and being under 

 the necessity of coming to the surface at certain 

 intervals for the purpose of breathing, cannot 

 fail to strike even the most unobservant mind as 

 being something quite beyond the ordinary. 

 Moreover, the momentary glimpses which in 

 general are all we obtain of these animals, and 

 the halo of mystery which still to a great 

 extent enshrouds their mode of life, are likewise 

 important elements in generating the wide- 

 spread interest they arouse. To the zoologist, cetaceans 

 are indeed not only of prime importance as being the sole 

 mammals which have assumed a purely fish-like form, and 



have become so thoroughly adapted to a completely pelagic 

 life as to be unable to exist on land, but their study gives 

 rise to many problems as to their origin and relationships, 

 and the mode in which they attained their present con- 

 dition. 



As we have already alluded to some of the leading 

 external features of cetaceans in our articles on " Swim- 

 ming Animals," we need not enter very fully upon these 

 here ; merely pointing out that while the general contour 

 of the body is fish-like, the tail-fin, or flukes, differs 

 essentially from that of a fish in being horizontal instead 

 of vertical ; while in place of the two sets of paired fins 

 characterizing a fish, a whale has but a single pair of 

 flippers representing the greatly modified fore-limbs of other 

 mammals. The hind limbs have, indeed, been completely 

 lost externally, although more or less imperfect traces of 

 them may still be detected deeply imbedded among the 

 muscles of the body. In the great majority of the group 

 the back is furnished with an upright fin, very similar in 

 appearance to the unpaired back-fin of a fish. Whereas, 

 however, such a dorsal fin is constantly present in fishes, 

 in cetaceans it may be absent or present in diflerent species 

 of the same genus ; while if we were to cut through such a 

 fin we should find a total absence of the slender spine-like 

 bones characterizing those appendages in a fish ; a similar 

 condition also obtaining in the flukes. In marked contrast 

 to the scaly armour of the majority of modern fishes, the 

 skin of a cetacean is for the most part completely naked ; 

 although the frequent presence, in the young state at 

 least, of a few scattered bristles in the region of the mouth 

 is of itself sufficient to indicate the derivation of these 

 strangely modified creatures from more ordinary mammals. 

 As regards their coloration, we may again, however, note 

 a similarity to most pelagic fishes, in that while the upper 

 parts are generally dark, the lower surface of the body is 

 of a light hue ; this arrangement being, of course, designed 

 to render all these animals as inconspicuous as possible 

 when viewed in the water either from above or fi-om below. 

 Although the flippers show no external indications of 

 digits, and are unprovided with nails, yet their internal 

 skeleton comprises the same elements as occur in the 

 limbs of any ordinary mammal, and is thus quite different 

 from that of a fish. This structural similarity is, however, 

 to a certain degree obscured by the alteration in the form of 

 the bones, and also by the circumstance that the number 

 of joints in the skeleton of the individual digits is increased 

 beyond the normal. As external ears would be mere 

 useless incumbrances, these appendages are absent ; while 

 the aperture of the ear itself is reduced to an extremely 



Fig. 1.— The Bridleil Polpliin. (From True, Bnll. T. S.Xaf. Museum.) 



minute size. To prevent the ingress of water during the 

 periods of submergence, the apertures of the nostrils, which 

 mav be either double or single, can be completely closed 



