Pisces. 



159 



over the outside of the 

 filament. The blood 

 entering the gills has 

 lost oxygen in passing 

 through the muscles 

 and other working tis- 

 sues of the body ; so, in 

 passing through the 

 gills, -it absorbs oxygen 

 from the water through 

 the comparatively thin 

 wall that separates it 

 from the water. On the 

 other hand, the blood 

 entering the gills is 

 loaded with carbon di- 

 oxid and other waste 

 matter that it has 

 picked up in the mus- 

 cles and other tissues ; 

 this passes out into the 

 water and is carried 

 away. It should be 

 noted that the current 

 of water is in the right 

 direction to keep the 

 delicate gill fringe 

 evenly extended, in- 

 stead of matting and 

 tangling it together, as 

 it would be likely to do 

 if the water current 

 were reversed. 



