THE LOWEST VERTEBEATES. 



LAMPREYS AXD HAG-FISHES. 



The great sub-kingdom of the Vertebrates, to the consider- 

 ation of which the present volume is restricted, draws its 

 lowest subjects from the ranks of these small and remark- 

 able creatures, which, presumably from a consideration of 

 their watery habitat, it was formerly the custom to include 

 among fishes — a habit that has taken such deep root that 

 one group still retains the title of hag-fishes. The dis- 

 tinctive features of this class are the absence of jaws, the 

 single opening of the nostrils, and the curious pouch-like 

 character of the gills, which are without arches. The 

 skeleton is cartilaginous, and the skull is closely joined 

 to the vertebral column. 



I. The Lampreys. 



Of the true lampreys we have three forms. The largest 

 of these, the Sea-Lamprey, is an inhabitant of salt water, 

 tsea- but enters many of our rivers, the Severn 



Lamprey, among them, for breeding purposes. It grows 

 to a length of about 3 feet and a weight of 5 lbs., and its 

 colour is usually some shade of grey or green, spotted with 

 black. The young, which remain for some years in fresh 

 water, their growth being very gradual, are toothless and 



