MINOT : SINUSOIDAL CIRCULATION. 
1<S7 
and saj^s “ sie besteben aus einer epithelialen Wand und einer 
Bindegewebshtille.” He says nothing as to the vascular endothe¬ 
lium; it will probably be found that Midler’s “ Bindegewebshtille ” 
is really endothelium, for this interpretation is certainly correct for 
Petromyzon. W. F. R. Weldon, ’84.3, p. 178 and Fig. 7, speaks 
of the wide blood spaces “ as an exceedingly rich plexus of blood- 
capillaries; so that during life a very considerable quantity of blood 
must be constantly passing between the tubules of the gland.” His 
Fig. 7 shows the vascular endothelium following the curves of the 
tubules, but not in actual contact with the epithelium; this separa¬ 
tion was probably due to imperfect preservation. Still more definite 
are the statements of J. W. Kirkaldy, ’93.1, p. 354, in regard to 
Myxine. He says, “Examined by means of transverse sections, the 
head kidney is found to be in very intimate relations with the post¬ 
cardinal vein. The greater part of it is actually lodged in the vein, 
while the more superficial tubules are imbedded in the vascular wall, 
or lie free in the pericardial cavity.” Unfortunately, neither in his 
text nor his pictures is there any record of the relation of the 
venous endothelium to the pronephric tubules. R. Semon, ’96.1, 
p. 178, also points out that in Myxine the pronephros protrudes 
into a venous sinus, and his figures 6 and 7 suggest that the endo¬ 
thelium fits the epithelium, but he gives no definite information. 
Otto Maas, ’97.1, p. 486, gives no precise description of the rela¬ 
tion of the endothelium to the tubules, but his figures, 20-23, repre¬ 
sent it as closely fitted to the epithelium of the tubules and of the 
ciliated funnels, precisely as in Petromyzon,— see Fig. 1, below. 
Concerning the histological structure of the pronephros of Petro¬ 
myzon, I have sought in vain for a modern description. [Since the 
completion of this manuscript, I have received' Wheeler’s valuable 
article, ’99.1, in which the character of the blood spaces, the fitting 
of the endothelium to the pronephric tubules in Petromyzon, is 
briefly mentioned and well figured by the author. My own observa¬ 
tions have now become hardly more than repetitions of a part of 
Wheeler’s.] The general topography is described by older writers, 
as, for instance, Johannes Muller and IT. Rathke. W. Muller, in his 
well-known monograph, ’75.1, pp. 120-125, describes with charac¬ 
teristic clearness and accuracy the “Vorniere” of Petromyzon 
fluviatilis and planeri. He does not give, however, a sufficient 
account of the relation of the vascular channels to the pronephric 
tubules. The advance in technical methods since 1875 has ren- 
