112 THE EVOLUTION OF MAN. 



rhina, we might further mention the presence of a sym- 

 pathetic nerve-system, a spleen, a ventral salivary gland ; 

 organs which are not represented in the lower Vertebrates 

 already considered. All these important parts have trans- 

 mitted themselves from Fishes up to Man, and from this 

 circumstance alone it is evident how wide a chasm sepa- 

 rates the Fishes from the Skull-less and Single-nostrilled 

 Animals (Acraniota and Monorhina). Fishes and Man 

 possess all these characters in common (Table X.). 



Turning now to consider the Fish class in greater detail, 

 we may divide it primarily into three main groups, or sub- 

 classes, the genealogies of which are evident. The first 

 and most ancient group is that of the Primitive Fishes 

 (Selachii), the best-known extant representatives of which 

 are the members of the much-varied orders of Sharks and 

 Rays (Figs. 191, 192). These are followed by a series of 

 further developed Fish forms, by the sub-class of Mucous 

 Fishes (Ganoides). The greater number of these have long 

 been extinct, and only very few living representatives are 

 known ; these are the Sturgeon and Huso of European seas, 

 the Polypterus of African, and the Lepidosteus and Amia 

 of American rivers. The earlier abundance of forms belong- 

 ing to this interesting group is, however, proved by the 

 abundance of their fossil remains. From these Mucous 

 Fishes originated the third sub-class, that of the Osseous 

 Fishes (Teleostei), to which belong most extant Fishes, espe- 

 cially nearly all our river fish. Comparative Anatomy 

 and Ontogeny very clearly show that the Ganoids sprang 

 from the Selachii, just as the Teleostei sprang from the 

 Ganoids. But, on the other hand, a second side-line, or 

 rather the main ascending line of the Vertebrate tribe, 



