Fig. 18. Taken from a transverse section .47 mm. caudad of Fig. 16 as 

 seen from the rear (caudad). Continuation of the right caudal sinus is 

 observed in section a little below the vertebral column as the caudal trunlc 

 (C. T.). The fin portion of the caudal trunk (C. T.), or the continuation of 

 the ventral trunk, is becoming more and more dorsal in the basal canal of 

 the caudal fin, and branches to it from the fin (C. R. C.) are seen in section, 

 as are also the corresponding arteries and veins. Both caudal arteries and 

 the caudal vein retain their former positions. X 9. 



Fig. 19. Transverse section taken through the caudal fin 1.18 mm. caudad 

 of Fig. 18 as viewed from the rear (caudad). Caudal vein and caudal trunk 

 will be found passing through the basal canal of the fin; the caudal ray 

 vessels are seen in section ; while the caudal artery has not yet left for the 

 basal canal of the fin. x 9- 



Fig. 20. One of the hremal trunks from a cross section through the caudal 

 peduncle of a 90 mm. L. osseus. Like the caudal vein, it is composed of a 

 single layer of endothelium, and no corpuscles of any kind were found for a 

 distance of several millimeters, x 225. 



Fig. 21. From a transverse section through one of the lateral trunks of a 

 90 mm. L. osseus as it sends inward a connecting vessel (C) to join the 

 haemal trunk. Note that the walls of both the lateral and the connecting 

 vessels, which are composed solely of endothelium, are bounded by a fibrous 

 connective tissue. Also that the red corpuscles greatly outnumber the white. 

 X 225. 



Fig. 22. A portion of a transverse section through a 90 mm. L. osseus, 

 showing the caudal artery and upper part of the caudal vein imbedded in a 

 mass of loose connective tissue within the hpemal canal. Corpuscles are very 

 abundant in the artery, while in the vein they are very scarce. Note that 

 the caudal veins consist of but a single layer of endothelium, which is almost 

 Identical with the hirnial tnmks. X 225. 



