256 RICHARD E. SCAMMON 



mosis. The blood vessels pass among the tubules covering them 

 in part with a thin film of endothelium which is interrupted at 

 soixie places by the attachment of strands of mesenchyma and at 

 others by the apposition of the distal surfaces of tubules with 

 the insheathing layer of splanchnic mesothelium. Whether this 

 endothelial covering forms an absolutely continuous partition 

 without fenestra between the blood and the tubule epithelium 

 cannot be definitely determined without injected specimens, 

 but there seem to be places where the separation is not complete. 

 Anastomosis is inaugurated by the contact of the involved tubules. 

 At first a few mesenchymal or endothelial cells may separate the 

 tubules but these are apparently pressed to either side so that the 

 entodermal cells soon lie in actual contact. Often at first only 

 four or five tubule cells actually meet, but shortly there is formed 

 an area of contact which generally is not quite so large as the 

 caliber of either tubule involved. Sometimes the cells of one 

 tubule indent the wall of the consort but this is not the common 

 rule. There are no basement membranes about the hepatic 

 tubules, but the basal margins of the cells seem a little thickened 

 so that for a time after contact the line between the cells of the 

 two anastomosing tubules is still distinct. With the disappearance 

 of this line the tubules may be considered as fairly fused. 



The connection between the two fused tubules is often drawn 

 out a little forming a short stalk or bridge between them. This 

 will be termed here the connecting stalk. An indentation upon 

 the external surface of this stalk indicates the line of fusion of the 

 tubules. The connecting stalk, when present, is generally a little 

 less in diameter than are either of the tubules and the boundaries 

 of the cells forming it are not clear. One can follow the cells, 

 however, by the position of their nuclei. Although at first sight 

 the nuclei appear scattered without order in the stalk or at the 

 point of anastomosis, a little study enables one to determine with 

 some accuracy which nuclei are contributed by each tubule. 

 The two rows of nuclei approach one another and may interlock 

 but their radial arrangement in regard to the lumina of the two 

 original tubules is not lost at first. They then pass to one side 

 or the other of the connecting stalk, leaving a clear cytoplasmic 



