HIGH SCHOOL ZOOLOGY. 



63 



young, and is only afterward closed. It is filled with air from 

 ceiitain blood-vessels which are so arranged as to allow an in- 

 terchange between the gases of the blood and those of the air- 

 bladder. However great the difference in this way between 

 Physostomous and Physoclystous Teleosts, yet there are some of 

 the latter which are transitional in other respects. The family 

 of the Scomberesocidae recalls both the Pikes (Esocidae) and 

 the Mackerels (Scombridae). In addition to the long-billed 

 marine Gar-fishes, several interesting species of Flying-fish, 

 Exocoetus (Fig. 30), belong to it, marked by the great size of the 

 pectoral (and ventral) fins. These creatures throw themselves 

 out of the water by means of the strong muscles of the tail, and 

 sustain themselves in the air by spreading the fins. 



Fig. 3'\— California Flyinf,' Fish. Exocoetus Californiensis. J. 

 (U. S. F. C.) 



16. Before discussing the ty|ncal Physoclystous lishes a passing refer- 

 ence may be made to certain aberrant forms A\hich attract attention by 

 the peculiarity of their shape. The Pipe lishes (Sjoignathus), and Sea- 

 horses (Hippocampus) (Fig. 31), agree with each other in the sti'ucture of 

 their gill-tilaments, which are arranged in tufts (Lophobranchii). like the 

 teeth of a comb. The snout is much produced, the mouth toothless and 

 the gill-cover a single plate. The Tobacco-pipe fishes (Fistularla) have 

 the ordinary gill-structure, but share the elongated body and produced 

 snout of the pipe-fishes. Allied to them are the Sticklebacks (Gasteros- 

 teidse) of fresh and brackish waters (Fig. 32), a group of tiny pugnacious 

 fishes which live on the fry of larger fish, but take care of their own in a 

 nest which is constructed and defended by the male. Some of the 

 species have regular bony plates on the side of the body : these however, 

 are absent in our common nine-spined and Brook Sticklebacks. 



