270 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
marked in the embryos of man, the cat, the rabbit, and the chick. 
Hence it seems to me fair to suppose that this feature is character¬ 
istic of the mesonephros of all amniote embryos, and marks a sharp 
distinction to be drawn between the mesonephros and the true 
kidney or metanephros. 
It is inevitable to deduce the supposition that the mesonephros 
has no true intertubular capillaries in any species, not even in such 
types as preserve the mesonephros as the renal organ of adult life. 
Attractive as this supposition appears, it is evidently necessarily to 
be tested by more accurate and extended observations than are yet 
at our disposal. 
Material already at my command enables me, however, to state 
positively even now that in the frog (Rana esculenta, R. lialecina) 
the blood channels are not true capillaries but irregular spaces 
bounded by an endothelium, which is closely fitted against the 
Part of a section of the mesonephros of Rana to illustrate the sinus-like 
arrangement of the blood vessels and the absence of true capillaries. For 
clearness the nuclei of the vascular endothelium are drawn dark. 3T.8 
