THE BREATHING APPARATUS, ETC., OF FISH 23 



Fig. II. 

 Bones of Head of the Perch. 



(After Giinther.) 



then divides into 

 fine capillaries, in 

 which the blood 

 is oxygenated and 

 returns purified 

 into the circulatory 

 system. 



The water, 

 having supplied the 

 gills with oxygen, 

 passes out through 

 the gill-cover, 

 which, in most 

 Teleosteous fish^ 

 takes the form of 

 a slit, marking the division between the head and the trunk. 

 It is protected by a thin, bony, external plate, called the oper- 

 culum (Figs. I. and II., 28), which with other bones, termed, 



from their posi- 



tion relative to 

 it, the prasoper- 

 culum {Ibid., 30), 

 the suboperculum 

 [Ibid.^ 3 2), and the 

 interoperculum 

 {Ibid., :>,i;), form 

 the gill-cover. 



Now the gills 

 are very delicate 



organs 



fish 



Fig. III. 

 Bones of Part of Head of the Perch. 



(After Giinther.) 



which may recover 

 from frightful 



external injuries 

 succumbs to a 

 compara t i vely 



