PEDIGREE OF MAMMALS. 279 



any special affinity between the otter and tlie seal, the 

 comparison of the two will aid us in imagininc; how from 

 true beasts of prey and terrestrial animals the stranf^c 

 figure of seals and walruses must have proceeded. 



If the conjecture already propounded should be 

 confirmed, that the detachments and ejections of 

 the placenta, which constitute the phenomena of the 

 decidua, assume very heterogenous 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 represent- 

 ing the extreme forms, but to discover the points of 

 derivation and attachment. Fossil whale-like animals 

 are known in the Tertiary period, such as the Zeuglo- 

 don and Squalodon. The remains of the former colossal 

 genus are kept in good preservation at Berlin, where 

 Johannes Miiller discovered 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 consider- 

 able, 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 dimen- 

 sions of the skull, the Delphinoidoe are the oldest mem- 

 bers of the true Cetacea. They were joined by the 



