02 JESSE LE ROY CONEL 



Semon ('97) regards this mass as the glomeruU of the head- 

 kidney. Eventually, however, the pronephros becomes trans- 

 formed into a suprarenal body. He found the mass rich in blood 

 vessels. 



Spengel ('97) thinks this mass was never glomerular, but that 

 it is either a suprarenal body or a lymph organ, and that it is 

 the result of a metamorphosis of the inner ends of the pronephric 

 tubules. 



Maas ('97) thinks the mass differs distinctly from a glomerulus. 

 Blood vessels occupy only a little space in it, and it is greatly 

 dissimilar to tubule epithehum. It resembles stages in the de- 

 velopment of the Miillerian duct of higher animals, especially 

 reptiles. It is also not unlike the medulla of suprarenals. 



Price ('10) evidently saw this mass, but does not describe it. 

 He states that '4n places the wall of the duct may become 

 greatly thickened by an increase in the number of epithelial 

 cells. These change their shape, and become much more loosely 

 arranged, so that the tissue loses entirely the structure of colum- 

 nar epithelium." Price adds that these thickenings are not 

 suppUed with arteries. 



In specimens with a duct which is continuous throughout the 

 entire length of the pronephros, the central mass appears only 

 in the posterior third of the pronephros where it surrounds the 

 duct and lies in the pronephiic vein. In most of the specimens, 

 however, the duct is broken up into segments which are not con- 

 nected with each other, and that part of each segment which 

 lies in the vein is surrounded by the central mass. The mass is 

 found only in the pronephric vein (a very small quantity may be 

 connected with the duct immediately before it enters the vein). 

 A typical distribution of the mass is represented by figure 12. 

 It may project into the vein like a glomus, one side remaining in 

 contact with the base of the pronephros, or it may lie in the lu- 

 men of the vein, completely surrounded by blood, and may be 

 attached to the base of the pronephros at one end only. The 

 central mass is found only in connection with the central duct 

 and is always attached to the latter, though one end of the mass 

 ma}^ extend in the j^ronephric vein some distance (as much as 



