202 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
capillary development, and such a development seems wholly 
impossible, since the organ is without mesenchyma. 1 All the blood 
vessels are merely subdivisions of the venous channel, and the sub¬ 
division is due to the complicated and perfect intercrescence of the 
wall of the vein on the one hand, and the liver epithelium on the 
other; these two tissues alone form the embryonic liver. The 
sinusoids thus produced at first increase in size, as we have 
seen occurs also in the pronephros and mesonephros ; subsequently 
they are gradually reduced, the reduction going far beyond that 
indicated in Fig. 8, continuing, as is well known, until they appear 
in the adult as the small so-called “ capillaries.” If the term pro¬ 
posed in this article for the class of vessels we are studying, be 
adopted, the vessels of the adult hepatic lobule can be distinguished 
as capilliform sinusoids. That the transformation of the large 
vessels of the embryonic liver in part into the small “ capillaries,” 
ciuct., of the adult has been long known, the following quotation 
from Toldt and Zuckerkandl, ’76.1, p. 266, will show :■— 
“ Nach Allem, was wir gesehen haben, sind die Capillargefassen 
der Leber in den frtihen Embryonalstadien, ansehnlich weiter als 
in den spateren, und zwar sowolil absolut, als namentlich im 
Verhaltniss zu den von ihnen umschlossenen Driisenbestandtheilen. 
Nocli melir tritt dies der Leber des reifen Ivindes gegeniiber 
liervor.” 
Comparatively late in the development of the liver, the connec¬ 
tive tissue dissepiments make their appearance. In this connective 
tissue in the adult occur true capillaries, which receive their blood 
supply from the hepatic artery. Although, apparently, nothing is 
known of their actual development, it may be assumed safely that 
they have genetically nothing in common with the capilliform sinu¬ 
soids of the portal circulation. 
In view of Alexander Goette’s well-known statement, ’75.1, that 
the first blood channels of the amphibian liver are without endo¬ 
thelium, further study seems necessary to ascertain how far in this 
class the circulation of the organ conforms to the sinusoidal type. 
4. Heart. We have seen in the three organs studied that the 
anlage of the organ first develops alongside an embryonic vein, then 
by intercrescence of the cells of the organ with the endothelium of 
the vein, sinusoids arise. The cells of the organ are separated 
1 There seem to be a very few cells of possibly mesenchymatous nature in the earliest 
anlage, chicks of 96 hours. 
