THE BREATHING APPARATUS, ETC., OF FISH 23 



FIG. II. 

 BONES OF HEAD OF THE PERCH. 



(After Gunther.) 



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 praeoper- 

 culum (Ibid.^ 30), 

 the suboperculum 

 (Ibid., 3 2), and the 

 interoperculum 

 (Ibid., 33), form 

 the gill-cover. 



Now the gills 

 are very delicate 

 organs ; a fish 

 which may recover 

 from frightful 



external injuries 

 FIG. III. , 



succumbs to a 



BONES OF PART OF HEAD OF THE PERCH. 



(After Gunther.) comparatively 



