76 Practical Zoology. 



n. Back of the oviduct or hinder part of the spermaries is a 

 small, pink (sometimes pale green) sac, the urinary bladder. Look 

 for its external opening back of the anus. 



12. Gently separate the parts of the digestive tube, and remove 

 any fat that is in the way. Make a diagrammatic sketch of the 

 digestive organs as seen from the ventral aspect, showing and 

 labeling the stomach, intestine, ceca, and the anal opening. 



13. Turn now to the pericardial cavity and examine the heart. 

 The red, angular portion of the heart, which in the natural posi- 

 tion of the fish lies lowest and hindmost, is the ventricle ; the 

 darker, more irregular portion lying (in the natural position) 

 above the ventricle, is the auricle ; the larger blood cavity back 

 of the auricle, and extending across the body cavity, above the 

 false diaphragm, is the venous sinus ; in front of the ventricle is 

 the light-colored conical arterial bulb. This narrows forward into 

 an artery which gives off branches on both sides, one to each gill. 

 Make a drawing of the heart and arterial bulb. After passing 

 through the gills, the blood tubes unite to form the dorsal aorta, which 

 passes backward just underneath the spinal column. From above 

 the gills branches also run forward to the head. Cut away and 

 remove the liver, stomach, intestine, and ovary (or spermaries). 



14. In the dorsal part of the body cavity is the air bladder. 

 Carefully scrape away some of the thin peritoneal covering and 

 note the thin, transparent wall of the air bladder itself. Scrape 

 away as much as possible of the peritoneum covering the air 

 bladder, in order to see if there are any blood tubes in the walls 

 of the air bladder. Make a puncture in the center of the air 

 bladder. What is the result ? Slit the air bladder along most of 

 its length and explore its extent and relations. Except on its 

 ventral surface it is attached to the inside of the walls of the 

 body cavity. 



15. Dorsal to the air bladder, extending along the roof of the 

 body cavity, are slender, dark red bodies, the kidneys. With 

 the forceps tear away the false diaphragm and as much as possible 

 of the air bladder. This should disclose the most distinct part of 



