HISTORY OF WHALES 



*93 



many peculiarities of detail that represent 

 a late stage of the telescoping process. 



Recent studies by Ridewood (192.2.) 

 on embryo skulls of highly telescoped 

 mysticetes confirm in a large measure the 

 general features of the palaeontological 

 evidence. Skulls of embryos exhibit a 

 rather broad intertemporal region formed 

 by the parietal bones. An interparietal 

 bone has been observed in the skull of a 

 9 inch foetus of Balaeriopera acuto-rostrata 

 and in a foetus of Balamopera borealis 

 measuring 3 feet 6 inches in length. No 

 sign of an interparietal bone was observed 

 in the skull of a foetus of Sibbaldus musculus 

 measuring 6 feet 4 inches in length or in 

 one of Megapera nodosa measuring 2.7 

 inches in length. In all of the above 

 mentioned embryo skulls, the parietal 

 bones have been pushed forward -across 

 the frontals. 



Embryology also furnishes the evidence 

 that the progenitors of the mysticetes were 

 provided with teeth. As many as 40 or 

 even more minute teeth with pin-like 

 crowns may be found hidden in the gum 

 on the maxillary of a foetal mysticete, 

 but they are soon resorbed. The atrophy 

 of the teeth was followed by the growth 

 of papillae (Tullberg, 1883) along the outer 

 margin of the upper jaw, and these 

 developed into a series of crosswise placed 

 corneous blades, the baleen. An inquiry 

 into the morphological features of the 

 mysticetes leads one to the conclusion 

 that many of the peculiarities of detail 

 were adjustments to unexpected condi- 

 tions associated with the procurement of 

 food. An abundance of soft-bodied crus- 

 taceans provided ample and readily obtain- 

 able food, which required no mastication, 

 but which did require some structure 

 adapted for catching such minute prey. 

 The blades of baleen are remarkably 

 well adapted for this purpose, and the 

 remodeling of the skull seems to have been 



profoundly influenced by their develop- 

 ment. 



ANATOMICAL AND PHYSIOLOGICAL 

 ADJUSTMENTS 



Adaptation to life in the water has 

 brought about many changes, as already 

 indicated, in the bodily organization of 

 cetaceans. We observe that the motive 

 power was transferred from the limbs, 

 which originally served as ambulatory 

 organs, to the hinder end of the body, 

 resulting in the development of caudal 

 flukes, which became the propelling 

 mechanism; the hind limbs disappeared; 

 and the fore limbs were modified into 

 fin-like organs, which served as rudders. 

 This adaptation is not a comparatively 

 recent biological phenomenon, for a 

 similar remodeling of the skeleton in a 

 group of marine reptiles, the ichthyosaurs, 

 took place at an earlier period in the 

 earth's history. Convergent develop- 

 ments of independent origin such as 

 these indicate that the remodeling of the 

 skeleton was governed by the operation 

 of some general principle of aquatic 

 adaptation. 



Flippers of whales bear little resem- 

 blance to the fore limbs of land mammals, 

 for they are overlain with blubber and are 

 fashioned like a paddle with margins 

 hardened by fibro-cartilage. Neverthe- 

 less they are supported and constructed 

 with similar bones, muscles, blood vessels, 

 and nerves. The hand has been remodeled 

 to conform to the use to which it is put. 

 The wrist bones have lost their original 

 shape and occasionally fuse into a compact 

 mass in old individuals. There has been 

 a reduplication of the bones in the fingers, 

 which has been variously explained as the 

 result of a secondary division of the strand 

 of cartilage attached to the terminal 

 phalanx, of intercalary syndesmoses, of 

 of double epiphysis formation (Kiiken- 



