PEDIGREE OF MAMMALS. 



279 



affinity between the otter and the seal, the comparison of 

 the two will aid us in imagining how from true beasts 

 of prey and terrestrial animals the strange figure of seals 

 and walruses must have proceeded. 



If the conjecture already propounded should be con- 

 firmed, that the detachments and ejections of the placenta, 

 which constitute the phenomena of the decidua, assume 

 very heterogeneous forms in groups belonging to the 

 same family, and may be alike in others no more nearly 

 related, the Cetacea would be installed in our pedigree 

 in the vicinity of the beasts of prey. Between a lion and 

 a whale an angle is enclosed, containing a countless 

 multitude of intermediate forms. But we must always 

 bear in mind that our business is, not to bridge over 

 the chasms between the present peripheral ends of the 

 series of development representing the extreme forms, 

 but to discover the points of derivation and attach- 

 ment. Fossil whale-like animals are known in the Ter- 

 tiary period, such as the Zeuglodon and Squalodon. 

 The remains of the former colossal genus are kept in 

 good preservation at Berlin, where Johannes Miiller dis- 

 covered their relations to both seals and whales. The 

 dentition is seal-like: in the skeleton there is much 

 similarity with the whales; and although the Zeuglodons 

 must have been preceded by a great series of species, 

 and followed by another of considerable, if not equal, 

 length, before the present Cetacea proceeded from them, 

 a development of this sort seems, nevertheless, extremely 

 probable and natural. By their still perfect dentition 

 and the still proportionate dimensions of the skull, the 

 Delphinoidae are the oldest members of the true Cetacea. 

 They were joined by the sperm whales or cachelots 



