198 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
die ersten soliden Lebercylinder an dem linken Gauge, d. h. kurze 
solide Epithelialsprossen desselben, und zugleich bilden sich von 
den anliegenden Venae omphalo-mesenterieae aus zahlreiche Gefass- 
sprossen in den grosser werdenden Leberwulst hinein. Gefasse 
und Epithelsprossen durchwachsen sich gegenseitig, und entsteht 
alsbald das typische Aussehen der jungen embiyonalen Leber: ein 
Geriist netzartig yerbundener Epithelstrange, dessen Ltlcken ganz 
von den relativ weiten, von platten Epithelien begrenzten Gefassen 
ausgefiillt sind.” 
Although the fact that the main circulation (portal) arises as a 
modification of a vein, by subdivision of the venous cavity and the 
intercrescence of venous endothelium and hepatic cylinders, has been 
long and familiarly known, yet no deductions seem to have been 
made. On the contrary, the custom is literally universal to speak 
of the “capillaries” from the portal vessels through the hepatic 
lobule to the axial (or so-called central or intralobular) vein. But 
these “ capillaries ” are obviously in no sense homologous with the 
true capillaries, and, moreover, probably differ as much from true 
capillaries physiologically as they do morphologically. The “ capil¬ 
laries” auctorum of the hepatic lobule are true sinusoids. The 
establishment of this conception appears to me an important gain in 
anatomical science. 
It is extremely easy to satisfy oneself by examining a series of 
embryos of a given vertebrate that the original wide sinusoids of the 
liver are transformed by the continual growth of the hepatic 
cylinders into smaller and smaller blood spaces, leaving, of course, 
certain wider channels as vascular trunks. Acanthias and the chick 
are particularly favorable types for the study of these changes. I 
will, since the essential facts are well understood, content myself 
with an enumeration of the principal stages in the two types men¬ 
tioned, so far as covered by my personal observations. First, 
Squalus acanthias. The brief account of the development of the 
liver in elasmobranchs given by F. M. Balfour in his monograph 
(See “ Works,” vol. i, p. 453) is correct. The liver arises as two 
diverticula, which by outgrowths of their walls begin to form hepatic 
cylinders in stage K ( ScyIlium canicnla of 10 mm.).. In an Acan¬ 
thias embryo of 11.5 mm. (Harvard Ooll. No. 206, section 4£1) the 
first short hepatic cylinders are present; between them are the 
blood spaces derived from the vein, and the epithelium is already 
close against the surface of the liver cells. Precisely this relation, 
