J. L. Bremer 479 
distal ends. Beyond this the Wolffian duct can be traced anteriorly for 
some distance (through twenty sections), and still further anteriorly is 
found a second group of tubules, consisting of three rather indistinct, 
scattered units, not connected by a duct. The most anterior tubule 
lies at the level of the liver and opens by a funnel-shaped mouth into 
the celom. This smaller group of tubules belongs to a rudimentary 
pronephros. 
In conclusion, I wish to point out the chief differences between this 
embryo and those of the same general stage of growth already described. 
The most important is the presence of anterior and posterior neuropores, 
which were supposed to have closed in human embryos of this size, 
though known to be open in comparable embryos of the pig and rabbit. 
Next in importance, perhaps, is the large right auricle of the heart, and 
the double passage into it from the sinus venosus. Next, the growth of 
liver cells, not into territory occupied by a large vein, but into the mesen- 
chyma surrounding the intestine, where also are growing branches of the 
vitelline veins; from the intercrescence of cords of liver cells and venous 
channels, sinusoids would inevitably result. Finally the presence of a 
few pronephric tubules, and the tardy growth of the left Wolffian duct, 
which has not yet acquired an opening into the cloaca. Let me add once 
more that embyro is, histologically and anatomically, in excellent condi- 
tion, and as far as can be seen normal. 
ABBREVIATIONS USED. 
Al—allantois. 
An. pl.—anal plate. 
Ao.=aorta. 
Au.=auricle. (Rt. and It.) 
B. ao=bulbus aorte. 
B. w=body wall. 
Coe.=celom. 
D. C.=ductus Cuvieri. (Rt. and It.) 
Gr.= groove. 
Il. ar.=iliac artery. 
In.= intestine. 
Jug.—jugular vein. 
Li= liver. 
Lu=ung. 
Med. gr.—|medullary groove. 
Mes.—=|mesentery. 
Musc.—jmuscle plate. 
Nch.— notochord. 
