<54 



BACKBONED ANIMALS. 



parent form for three years. For an illustrated account of nest-building 

 fishes see the article on the subject by the author in " Harper's Month- 

 ly," Christmas number, 1883. 



FIG. 192. Figure of a full-grown lamprey and of the yourg lamprey, for- 

 merly called Ammoccetes, showing the seven holes through which it takes 

 in water to breathe. 



Class III. THE TRUE FISHES (Pisces). 



General Characteristics. Aquatic Vertebrates with a 

 cartilaginous skeleton, as in the shark, or a bony one, as 

 in the perch ; as a rule, scaled, and breathing by means 

 of gills ; limbs represented by fins. 



Skeleton. At first glance, the skeleton of a bony fish 

 (Fig. 193) seems to have two backbones ; the lower, how- 

 ever, is the vertebra, that extends from the head to the 

 tail. The upper series, f and <:, are median or middle fins, 

 supported by interspinous bones. The backbone is com- 

 posed of sometimes two hundred vertebrae in bony fishes. 



