94 JESSE LE ROY CONEL 



was found. Occasionally such nuclei occur in the walls of the 

 duct or of the tubules near the central mass. These giant nuclei 

 are much more deeply stained than are the other nuclei of the 

 mass, and the cytoplasm, which always surrounds them, stains 

 hke that of blood corpuscles, but much more deeply. These 

 giant cells are interpreted as greatly enlarged blood corpuscles. 

 They do not have the elongated characteristic shape of the blood 

 corpuscles, but are usually rounded and quite irregular in out- 

 hne. In the central mass they are surrounded by a very thin 

 membrane which is interpreted as endotheUum, although no nu- 

 clei were observed in it. In the walls of the duct or tubules, 

 however, nuclei occur in the membrane surrounding the giant 

 blood corpuscles and here it is undoubtedly endothelium. These 

 giant cells are also frequently seen in capillaries which occur in 

 the connective tissue surrounding the mesonephric duct, and 

 here there is no doubt that they are in blood vessels. 



Excepting the giant corpuscles just described, the writer 

 rarely found a blood corpuscle or blood vessel in the central mass. 

 An attempt was made to find blood vessels entering the mass, 

 but without success. The blood corpuscles have a distinctly 

 characteristic shape and appearance, and the cytoplasm stains 

 more deeply in eosin than that of any of the other cells in the 

 pronephros, hence the corpuscles are easily discerned in any tis- 

 sue. There are many spaces in the central mass, but they are 

 not lined by endothelium and never contain blood corpuscles. 

 Furthermore, the writer found no vessels leaving the central 

 mass to enter the vein or any surrounding tissue. Also, natural 

 appertures in the endotheUal wall of the mass were diligently 

 but vainly sought ; the mass is completely shut off from the blood 

 in the vein. One series of sections is especially well stained to 

 demonstrate this fact. The blood corpuscles are stained a deep, 

 yellowish-red, which is strikingly different from the pale blue of 

 the central mass. The blood corpuscles surround the latter as a 

 dense mass which almost fills the lumen of the vein. On account 

 of the striking contrast in stain, a single blood corpuscle inside 

 the central mass would be instantly recognized if present. But 



