FIG. 179. Diagram of the principal vessels in the circulation of a Fish, lateral view. 

 Lettering as in the preceding figure. Adapted from Parker and Haswell. 



Questions on the figure. Compare the two views (Figs. 178 and 179) 

 and identify the parts common to both, tracing the course of the circula- 

 tion in the various vessels. Put arrows in the figure to show your idea 

 of the course of the blood. 



379. Library Exercise. Find description and figures in the reference 

 zoologies locating the unfamiliar structures in the table on page 340 and 

 testing the statements found there. 



380. Habits and Food. Fishes occur abundantly both in 

 fresh and salt water. Usually the whole life is spent under 

 the same general conditions. The salmon and shad, however, 

 are bred and partly develop in fresh water and later pass out 

 to the sea. These forms return, often with remarkable pre- 

 cision, to the place of their own hatching to deposit their eggs. 

 Use is made of this habit in the capture of them for com- 

 mercial purposes. Unless some means are found for limiting 

 the destruction of the adults during the breeding period, some 

 of our most valuable food fishes are in danger of extermina- 

 tion. Others, as the eels, may generate in the sea and spend 

 a part or all their adult life in fresh water. Some burrow in 

 the muddy bottoms, as the eel, cat-fish, mud-fish; others lie 

 on the bottom, as the flat-fish ; many quaint forms frequent the 

 depths of the sea. The most are active swimmers in open 

 water near or away from the shore. Many forms (herring, 

 shad, salmon, etc.) are distinctly gregarious, moving in great 

 shoals especially at spawning time or when in search of food. 

 This fact and the knowledge of places and times are matters 



