196 RITTER: [Vou. XII. 
there seems to be in the section here represented a passing of 
cells from the wall of the vesicle into the Ax/age, pc.a., but the 
evidence of such a process is more convincing in this section 
than in either of the other three sections of the series in which 
the An/age appears ; and even here, as the figure shows, the 
line of separation between the wall and Ax/age is distinct in 
places.1 At the same time the cells of the Az/age are some- 
what more deeply stained than are the immediately adjacent 
ones in the wall of the vesicle, a fact which I have attempted 
to bring out in the figure by making the former slightly darker 
than the latter. Again, as seen by this figure, the cells of the 
Anlage are not closely massed together as one would suppose 
they would be had they been derived from the vesicle at the 
single point where, as shown by the figure, they are passing 
from the latter into the former. 
These two last-mentioned conditions raise some doubt about 
the origin of the Az/age from the vesicle, and at the same time 
they, together with the close resemblance of the cells compos- 
ing it to some of the surrounding mesenchyme cells, suggest 
these latter as being its source. I have not seen an earlier 
stage than this in the formation of the Av/age, but have found 
about the same and slightly older stages not infrequently, and 
in all cases the conditions presented are very similar. In Figs. 
69 and 71, Pl. XVI, are represented sections from different buds 
both considerably more advanced in development than that 
just described, though of the two the one shown by Fig. 71 
is somewhat older. Here the cavity of the pericardium is 
already established, though it is quite small, particularly in 
the younger bud. The portion of the wall of the organ in 
contact with the wall of the inner vesicle is thicker than else- 
where, and the two appear to be in organic connection ; but 
any one who has had experience in determining whether two 
cell masses in contact with each other are really organically 
connected or not, knows well how extremely easy it is to 
be deceived. I have carefully examined with an oil-immer- 
The interruption of the line separating the 47/age from the wall is at a point 
toward which the index line /c.a., Fig. 68, points. The lithographer has failed to 
accurately reproduce my drawing here. 
