n6 



ANIMAL BIOLOGY 



gill cover. These rays grow from the tongue bone. (Zu, 



Fig. 216. This is a rear view.) 



Watch a live fish and determine how the water is forced 



between the gills. Is the mouth opened and closed in the 

 act of breathing? Are the openings behind 

 the gill covers opened and closed ? How 



B 



FIG. 217. 



CIRCULATION 

 IN GILLS. 



FIG. 218. NOSTRILS, MOUTH, AND GILL OPENINGS OF 



STING-RAY. 



many times per minute does fresh water reach 

 the gills ? Do the mouth and gill covers 

 open at the same time ? Why must the water 

 in contact with the gills be changed constantly ? Why 



does a fish usually rest with its 



head up stream ? How may a 

 fish be kept alive for a time 

 after it is removed from the 

 water ? Why does drying of 

 the gills prevent breathing ? If 

 the mouth of a fish were propped open, and the fish re- 

 turned to the water, would it suffocate ? Why, or why not? 







a I 



FIG. 219. GILL OPENINGS OF 

 EEL. 



Food Tube. The gullet is short and wide. The stomach is 

 elongated (Fig. 220). There is a slight constriction, or narrow- 

 ing, where it joins the intestine. Is the intestine straight, or does 

 it lie in few or in many loops? (Fig. 220.) The liver has a gall 

 bladder and empties into the intestine through a bile duct. Is the 



