202 THE HISTORY OF CREATION. 



of all solid parts, could, unfortunately, as little as the 

 Skull-less animals leave fossil remains. From its whole 

 organization and ontogeny it is quite evident that it 

 represents a very important intermediate stage between 

 the SkuU-less animals and Fishes, and that its few still 

 existing members are only the last surviving remains of 

 a probably very highly developed animal group which 

 existed towards the end of the primordial period. On 

 account of the curious mouth possessed by the Hags 

 and Lampreys, which they use for sucking, the whole class 

 is usually called Round-mouthed animals (Cyclostoma). 

 The name of Single-nostriled animals (Monorrhiua) is still 

 more characteristic. For all Cyclostoma possess a simple, 

 single nasal tube, whereas, in all other Vertebrate animals 

 (with the exception of the Amphioxus) the nose consists 

 of two lateral halves, a right and a left nostril. We are 

 therefore enabled to comprise these latter (Anamnionata 

 and Amnionata) under the heading, double-nostriled animals 

 (Amphirrhina). All the Amphirrhina possess a fully 

 developed jaw-skeleton (upper and under jaw), whereas it 

 is completely wanting in the Monorrhina. 



Apart also from the peculiar nasal formation, and the 

 absence of jaws, the Single-nostriled animals are dis- 

 tinguished from those with double nostrils by many 

 peculiarities. Thus they want the important sympathetic 

 nervous system, and the spleen which the Amphirrhina 

 possess. Of the swimming bladder, and the two pairs of legs 

 — which all double-nostriled animals have, at least in their 

 embryonic conditions — not a trace exists in the Single- 

 nostriled animals, which is the ease also in the Skull-less 

 animals. Hence, we are surely justified in completely 



