128 MAMMALIAX DESCENT. [Lect. Y. 



mammalian forms of tliat time are more nearly related 

 to our existing Insectivora than to any of the grouj^s 

 that lie on a higher jDlatform or level. From some 

 such common root-stock one great sucker or stolon after 

 another arose : — Rodents, Bats, Hyracoids, Proljoscideans, 

 Herbivora, Sirenia, Cetacea, Carnivora, and Primates. 

 At first sight it might seem that the huge Whales 

 were more worthy to have been brought upon the scene 

 miraculously than the little Bats, but as both these 

 sorts of beasts are continually developing, even now, 

 from an almost infinitesimal pellet of j^rotoj^lasm, it 

 seems to me that the large types came into being as 

 easily as the small. Sjieaking of protoplasm, I may 

 remark that the mind is overwhelmed when it at- 

 tempts to follow the embr3"ology of one of the larger 

 Cetacea ; however its feats are accomplished, it must 

 be confessed that protoplasm has an amazing power 

 of growth. Whatever may be the difficulty as to 

 the gradual modification of a terrestrial form into one of 

 these swimming islands, there can be no gainsay to the 

 fact that each living Whale repeats its ancestral history 

 in its own lifetime, more or less. Anyhow, in this 

 present period, Whales exist, however we may account 

 for their existence. Can the lowly. Insectivora throw 

 any light upon the evolution of these huge types ? In 

 attempting to answer my own question I shall sjDcak 

 mainly of those diagnostic characters which are to be 

 found in the head ; these will be looked at both from 



