218 THE ELASMOBRANCH FISHES 



Moreover, Burne (1923) has shown for Lamna that well marked cutaneous 

 arteries do accompany some of these veins. Parker (1886) called attention to 

 the presence of blood in these vessels and Mayer (1888) proved that they are 

 provided with valves. Furthermore, the cutaneous vessels are put into direct 

 connection wutli the deeper veins, for example, the caudal vein. Also, Mayer 

 reported the circulation of blood in these vessels in a semitransparent embryo. 

 All the above points made it likely that these vessels are true blood-vessels. 

 The actual proof that they are haemal and not lymphatic in nature was made 

 by Edith Stoker (see Daniel and Stoker, 1927) in the following way. The 

 shark was first anaesthetized and a glass canula was inserted into a cut 

 through the lateral cutaneous vessel. In this experiment the blood will circu- 

 late through the canula, demonstrating that the vessels are for the circulation 

 of blood. 



Lymphatic Vessels 



Lj-mphatic vessels have been difficult to demonstrate in Elasmobranchs. 

 Within recent years, however, Hoyer (1928) has succeeded in injecting these 

 vessels, and reports that they have the following arrangement. Right and left 

 trunks (thoracic ducts) accompany the dorsal aorta from the tip of the tail 

 to the head. These trunks collect lymph from the muscles of the tail and trunk 

 through tiny branches which run with the intersegmental arteries. They re- 

 ceive lymph from other vessels which run with the arteries and veins along 

 the myosepta and the longitudinal septa separating dorsal and ventral 

 bundles. A net of these vessels is present under the peritoneum and over the 

 kidney. Lymphatics from the intestine unite in a plexus at the base of the 

 mesentery and these plexuses are put into connection with the thoracic ducts 

 through cross-trunks. In addition to these right and left ducts in the tail and 

 trunk, there are two jugular trunks in the area of the head and pharynx, 

 which accompany and finally enter the cardinal sinuses. Further, accompany- 

 ing the subclavian arteries there are two branches which also enter the cardi- 

 nal sinuses. 



