40 A MANUAL OF ZOOLOGY 



of the cloacal veins to the ductus Cuviei-I. It runs parallel 

 but ventral to the dorsal aorta. Open the heart through 

 all of the chambers by a ventral cut. Demonstrate the 

 valve between the ventricle and the auricle. Demonstrate 

 the pocket valves in the conus arteriosus. How many 

 transverse rows of valves and how maty valves in each 

 TOW in your specimen? Open the nasal cavity. Where 

 does it open posteriorly? Note carefully the lining of the 

 nasal cavity. Make a drawing of the circulatory system. 

 Expose the internal gills and make a diagram showing ttie 

 circulation in the gills. 



THE EXCRETORY AND THE GENERATIVE SYS- 

 TEMS — The kidneys lie in the posterior part of the body 

 cavity on each side of the spinal column and may be ex- 

 posed by carefully cutting away the peritoneum covering 

 them. They are long, flattish, lobulated (organs composed 

 of bunches or lobes of tubules. The tubules forming the 

 hinder portion of the kidneys are called the metanephros 

 or true kidneys. The tubules from these lobes unite to 

 form about six branches. These join one another to form 

 a duct, the ureter, which opens directly into the cloaca 

 in the "female and in the male .Into the paired uro-genital 

 sinus which empties into the cloaca. Demonstrate. The' 

 anterior part of the lobulated mass is known as the meso- 

 nephros. This is rudimentary in the female. In the male 

 the tubules serve to cariy the spermatozoa. Find in the 

 male, in the dorsal part of the dorsal cavity, two long 

 flattish bodies united with one another posteriorly. They 

 are the testes and are connected anteriorly by slen'der 

 tubes, the vas deferens which leads to the cloaca. Dem- 

 onstrate. The posterior end of the vas deferens is dilated 

 forming the vasicula seminalis. In the female look for 

 the single ovary in the dorsal part of the body cavity 

 suspended in folds of the peritoneum. Back of the vis- 

 cera, extending from a position near the posterior end of 

 the heart to the cloaca, are the two oviducts united in 

 front and opening by a single large aperture into the 

 body cavity. Notice an enlargement of each duct, the shell 

 gland. How do the ova get into the oviducts? Draw the/ 

 uro-genital apparatus. 



