206 RITTER. iVor. XT 
is not sufficient to prove that the ectoderm is not giving off 
cells into the body space at the tome when the Anlage ts being 
formed. It must also be shown that the process does not 
take place at any earlier time. But when it is considered that 
the An/age is formed at a very early stage in the life of the 
bud, it will be seen not to be a matter of great difficulty to 
examine a complete series of stages from the very inception of 
the bud up to the time when the Az/age is fully formed. This 
I have done repeatedly, that is, on numerous series of sections, 
and the description of the ectoderm already given applies as 
well to one stage as to another. To emphasize this fact I would 
again call attention to Figs. 68 and 74, ec., the first from a bud 
in which the Az/age has not yet appeared, the second from 
one in which it is forming. I thus hope to have successfully 
assumed the risk of posztively denying that the nerve ganglion 
comes from the ectoderm in the blastozootds of Perophora, even 
though I cannot be so positive as to what its source really is. 
Concerning the difficulties in the way of deciding whether the 
inner vesicle or the “‘mesenchyme’”’ cells are the real source of 
the Ax/age, I need only refer the reader to what has already 
been said about the difficulties involving the study of the origin 
of the pericardium. The well-nigh universal distinctness of 
the line of separation between the Az/age and the wall, the 
lack of compactness of the Az/age in its early stages, and the 
close resemblance of its cells to many of the surrounding blood 
cells, here, in the same degree as there, suggest the latter as 
being the source of the Anzlage. Fig. 72, Pl. XVII, affords a 
typical illustration of this. It is drawn from the section in 
which, if in any one of the series, the separating line is inter- 
rupted by cells passing from the wall to the Axlage. At 
the middle point of the separating line there seems to be such 
an interruption. 
By far the most convincing evidence that I have of the origin 
of the Anxlage from the vesicle consists of the occurrence in a 
single specimen of what is almost certainly az zmperfect evagt- 
nation by which itis formed. Fig. 74, Pl. XVII, represents the 
section in which this is most clearly seen. There is no 
doubt that the separating line is interrupted here at the point 
