PEDIGREE OF MAMMALS, 279 
any special 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 
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 Miller 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 Delphinoide are the oldest mem- 
bers of the true Cetacea. They were joined by the 
13 z 
