18 SATURDAY LECTURES. 



vanced forwards in tlic fish. The cerebellum of the fish 

 and cetacean have an entirely different structure, and as to 

 differences of detail, they are innumerable. 



Those parts which are concerned in tlie reproduction and 

 perpetuation of the species, are equally noteworthy on 

 account of the close resemblance between such parts in the 

 whales and in viviparous quadrupeds on the one hand, and 

 on the other, the differences from fish's. Their char- 

 acteristics, however, we must pass over. Suffice it to say, 

 that as in man, the whales are viviparous, and the young 

 are nourished by milk secreted by the mother. But it is 

 proper to add that such characteristics are of less importance 

 than many others connected with the organs of reproduction. 



Many fishes are also viviparous. Viviparity or oviparity 

 is of minor value. It is the mode in which the eggs and 

 young are developed that is most significant for tlie two 

 classes. 



Thus have we gone over the various parts of the economy 

 of the whale and the fish, and in every case we have seen 

 that the structure of the whale and man is very much 

 alike, and that of the fishes very different. 



If this superficial examination may be sufficient to con- 

 vince us of the similarity of the whale and all other 

 mammals, a more detailed examination would simply add 

 force, and the cogency of cumulative evidence to the argu- 

 ment, and would still more impel belief. 



Let us now take into consideration another set of facts. 

 There are certain forms known as marsupials, represented 

 in this country b}'^ the opossum. In Australia that order is 

 largely developed, and is manifested in a number of differ- 

 ent forms. There are, for example, species very much like 

 wolves, others like mice, and they are so called by the Aus- 

 tralian colonists. Now, if we considered simply external 

 form, we should be compelled to separate those species from 

 each other, and refer them to widely different groups. For 

 example, we should have to take the mice-like marsupials, 

 and approximate them to the true rats and mice, and the 

 Tasmanian wolf we would have to approximate to the gen- 



