NECTURUS 9 



and posteriorly to about the middle of the body cavity. Cut 

 into it near the liver, and with probe and scalpel trace the postcava 

 through the liver to the false diaphragm, noting the entrance of 

 small vessels, the hepatic veins, during its course. At about the 

 point where the postcava leaves its dorsal position to enter the 

 liver it connects with the hinder ends of a pair of postcardinal 

 ('azygos') veins into which pass small veins from the anterior 

 genital organs and the spinal region. 



Add these vessels to your sketch. 



Cut through the stomach at about the middle and through 

 the intestine in the pelvic region. Cut the alimentary canal 

 loose by trimming the mesogaster, mesentery, etc., close to the 

 intestine. Also remove most of the liver, leaving the anterior 

 portion, together with part of the postcava, attached to the 

 septum transversum. You can now study 



The Urogenital Organs. In the male these consist of the testes 

 and their efferent ducts together with the mesonephroi (the so- 

 called kidneys); in the females, besides the mesonephroi, of the 

 ovary and its ducts. Two specimens will be needed to make out 

 all the features. 



In the male the testes are a pair of solid oval bodies l}dng in 

 the posterior part of the roof of the body cavity. Each is sup- 

 ported by a fold of the peritoneum, the mesorchium, in which 

 blood-vessels, spermatic arteries and spermatic veins, may be 

 traced, the former coming from the dorsal aorta to the testes, 

 the latter passing from the testes to enter the postcava. Add 

 these vessels to the sketch of the circulation already made. 



Next find the ducts leading from each testis, the vasa efferentia, 

 these uniting to form a common convoluted tube, the vas deferens 

 or Leydig's duct. Trace this latter in both directions. How far 

 forward does it extend? This portion in front of the testis is 

 functionless. Sketch the reproductive organs on one side of 

 the body as far as made out. Then cut away the testis of the 

 opposite side. This will expose the mesonephros (Wolffian body) 

 lying between the vas deferens and the median line. Sketch this 

 and the related structures on the other side of the drawing. 

 Note that the mesonephros is narrower in front than behind. 

 See that the vasa efferentia pass through this narrower portion 

 in order to reach Leydig's duct. Farther back see the urinary 

 tubules leading from the mesonephros to Leydig's duct, which 



