144 



FIRST LESSONS IN ZOOLOGY. 



rows of conical, horny teeth ; the eyes are well developed. 

 Moreover., there is a dorsal fin. The brain is comparatively 

 well developed, though of a low fish-like grade, and it is 

 protected by a gristly brain-box, rudely anticipating a skull. 

 The breathing-organs or gills are very peculiar, being 

 purse-like cavities (whence the name of the class, Marsipo- 

 brancliii}, which in the lamprey are seven in number on 



FIG. 151. The Lamprey Eel. n, nostril. (J natural size.) 



each side of the pharynx, opening externally by small aper- 

 tures; internally they connect with a long cavity lying under 

 the oesophagus, and opening into the mouth. 



The lamprey lives both in fresh and salt water. The 

 eggs of the common lamprey, Petromyzon marinus (Linn. ), 

 are laid in early spring, the fish following the shad up the 

 rivers, and spawning in fresh water, seeking the sea in au- 

 tumn. 



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