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Show 1888.] MORPHOLOGY OF SUPERNUMERARY PHALANGES. 507 shows that the phalanges of the foetal Cetacean manus exceed in number those of the adultl; while the latter record the appearance of a supernumerary phalanx in that of the Sirenia. All subsequent investigation has confirmed Leboucq's observation, but it is at present uncertain how far the process of abbreviation may be the result of absorption or of concrescence. It is most interesting to recall, in view of this, Gotte's observations upon the limbs of Molge (his Triton). He shows (5. p. 12) : - " Es wurde schon her-vorgehoben, dass diese Endphalangen, namentlich an denLarven von T. cristatus, durch ihre Lange auffallen ; anfangs iibertreffen sie darin nicht selten die andern Glieder desselben Fingers, Metacarpus und Phalangen zusammengenommen. In der spatereu Sommerzeit wachsen sie weniger schnell, sogar langsamer als die anderen Glieder, behalten aber ein lang und spitz ausgezogenes Ende, welches auch der ganzen Fingerspitze die gleiche Form verleiht. Sie erhalten auch wie die iibrigen langen Knorpel eine aussere Knochenhiille, welche aber den dickeren proximalen Teil des Gliedes nicht iiberschreitet, so dass die grdssere Halfte des Knorpelfadens daraus frei hervor-hangt." He further shows that these filamentous terminal phalanges become abbreviated by atrophy (? absorption)2. Leboucq, commenting on this, writes (13. p. 533) : " diese Angaben glaube ich mit den von mir bei Cetaceen nachgewiesenen Thatsachen paral-lelisieren zu diirfen" ; but all subsequent observation does not fully bear this out, for Kiikenthal has more recently shown (10. p. 639) that adjacent proximal segments may coalesce3. These important observations indicate, when viewed in conjunction with our own, a general shuffling (if the comparison may be admitted) among the terminal phalanges, and their interest increases when it is said that Peters records (16. p. 6) a reduction in number, by concrescence, of the phalanges in the Chelonian Pelomedusa. Significant as are the above-cited discoveries, they do not help us towards an understanding of the primary origin of the supernumerary phalanges themselves. They deal only with metamorphoses and not with original development. It is well known that while, in the Odontocetes, the phalanges bear terminal epiphyses which articulate by means of imperfect synovial joints, in the Whalebone Whales they are less differentiated and united by fibrous tracts 4. The only serious attempt yet made to grapple with the question of primary origin of these parts is that of Ryder (17); he concludes (p. 1015) " that it has been through a Seal-like ancestry, with prolonged integuments to the manus, in which the nails were not terminal but dorsal, beyond which the ungual phalanges were extended as bars of cartilage, which gave 1 M a x Weber has denied this (19) on examination of Globiocephalus, but Kiikenthal has shown more recently (10. p. 643), upon examination of more extensive material, that he was in error. 2 Mr. Boulenger informs us that he has observed a similar phenomenon in certain other Amphibia. 3 Hi3 discovery that a similar fusion may go on between elements of the carpus not hitherto recognized is no less striking than Leboucq's. 4 Cf. Flower, 4. p. 272. |