MINOT: SINUSOIDAL CIRCULATION. 
191 
many times the diameter of a true capillary, and are bounded by an 
endothelium, showing very few nuclei, and fitted closely against 
the surfaces of the tubules and the pseudo-lymphoid masses. The 
pronephric tubules are almost completely surrounded by the blood 
channels. The blood enters the organ from the large vein at the 
caudad end of the organ, and passes out towards the heart through 
the large vein at the cephalad end. The study of this and younger 
stages shows that the territory of the pronephros is an interruption 
of the vein and that the structure figured is the result of a compli¬ 
cated intercrescence of the venous endothelium and the two tissues 
of the organ, in short, that the general scheme of development is 
the same as in teleosts. It should be added that Jungersen’s article, 
'94.1, on the kidney of Amia contains no data on the circulation. 
As regards other Ganoids, I have no personal observations to offer. 
In the memoir by Balfour and Parker, ’82.1, and in the two papers 
by Beard, ’89.2, ’94.2, there is no definite description of the cir¬ 
culation of the pronephros of Lepidosteus. Filrbringer, ’78.1, p. 59, 
has given a few data on the head kidney of Accipenser, but says 
nothing of the blood vessels. 
In regard to Teleosts, I need only repeat what I have said in my 
previous paper, J 98.1, p. 271. The specific sections there mentioned 
as being in the Harvard collection demonstrate the very close 
resemblance of the pronephros of Ameiurus and Batrachus to that 
of Amia, and reveal a typical sinusoidal circulation. 
The pronephros of Amphibia is better known than that of any 
other class of vertebrates. The large size and numerous free con¬ 
nections of the intertubular blood spaces, and the close fitting of 
the endothelium against the epithelium of the tubules, have been so 
often seen, described, and figured that there is no doubt that the 
circulation is sinusoidal. The pronephros of the very interesting 
American perennibranchiate (proteid) genus, Necturus, has not, so 
far as I am aware, been described. Fig. 3 is a section from a Nect¬ 
urus larva of 18.0 mm. The section figured passes through a 
nephrostome, nst , which I think is furnished with cilia, but as they 
are not clear in the preparation, which is stained only with alum 
cochineal, I have not drawn them in. The pronejdiros has a nearly 
circular outline and protrudes but slightly into the coelom, Coe. 
The blood sinusoids, Si, Si, occupy the entire intertubular space, 
and their epithelium is everywhere closely fitted to the tubular 
epithelium; the tubules in cross-section are nearly circular; their 
