ADULT HEAD KIDXEY OF BDELLOSTOMA STOUTI 857 
the group, the tubules become sHghtly smaller at the pericardial 
end, so that the nephrostome is the opposite of funnel-shaped. 
The tubules are formed of columnar epithelium which is con- 
tinuous on the one hand with the epithelium of the central duct 
and on the other with the flat pericardial epithelium. The tubules 
are ciliated, as could be clearly seen in part of the preserved 
material, and still more clearly in living material. W. Miiller, 
working with living material, was unable to find cilia in Myxinc, 
but Maas found them in his young specimens. Weldon did not 
find them in Bdellostoma fosteri. 
Lying between the tubules are sinusoids, which, as may be 
seen in fig. 2, are connected with the large veuous diverticulum in 
which the head kidney is in a way imbedded. These sinusoids, 
together with some small veins from the glomerulus to be men- 
tioned later, form the only blood supply found in connection with 
the main body of the gland. It should be mentioned, however, 
that no well injected ma'^erial was studied in sections. 
In the head kidney of Bdellostoma stouti, in the adult as well 
as in the embryo, there can be no question about the existence of 
a central duct. This is a point of some interest, since there is a 
difference of opiaion as to whether or not such a duct is present 
in M>'xine, the earlier workers, W. Miiller and Kirkaldy affirming, 
and the later workers, Semon, Spengel and Masa denying i:s 
existence. Maas's work on young individuals seems to prove 
conclusively the correctness of the latter view. In the embyro 
of Bdellostoma stouti the duct in some cases fails to develop 
between some of the anterior tubules. If this should be carried 
far enough it would result in the forma do a of a ductless head 
kidney. Perhaps this is the explanation of the condition found 
in Mjrxine. Weldon describes a central duct for the head kidney 
of Bdellostoma fosteri. His figures seem to prove that he was 
correct, although Semon, working on a single poorly preserved 
specimen, came to the conclusion that Weldon's duct was in reality 
a venous sinus. 
The duct may be continuous throughout the length of the 
head kidney, and may even extend a little beyond it at the poste- 
rior end; or it may be broken into two or more distinct parts: 
