152 Gastrulation and Embryo Formation in Amia Calva 
toderm yon der spiiter zu Mesoderm und Entoderm werdenden Zellage— 
Sehr bald beginnt nun am Aequator des Keies die Urdarm-Bildung, und 
zwar zuerst an der Stelle der spateren Embryonalanlage. Es entsteht 
dadurch die dorsale Urmundlippe (Fig. 4). lLetztere ist zur Zeit, wo 
der Urdarm als feiner Spalt sichtbar wird, sofort deutlich dreiblattrig, 
nicht zweiblattrig wie Dean angiebt. Die verschiedene Gehalt der Zellen 
an Dotterkérnern, resp. die verschiedene Groésse derselben in den Zellen, 
ermoglicht die Unterscheidung drier Keimblatter sehr leicht.” The 
writer then points out the differences in the sizes of the granules in the 
different layers, stating that those in the cells of the ectoderm are all 
fine, those in the cells of the mesoderm are considerably larger, while 
those in the cells of the entoderm are coarse. The writer further states 
that when the gastral cavity has extended beneath the dorsal lip of the 
blastopore, the dorsal and ventral mesoderm are united. 
It is evident from our studies that we agree in general with Sobotta in 
that we find the ectoderm early separated from the underlying layer of 
cells by the slit-like remains of the segmentation cavity. This underlying 
layer represents, according to Sobotta, the mesoderm. We do not agree, 
however, that in the early gastrula the size of granules or their staining 
capacity will enable one, as Sobotta claims, to distinguish mesoderm 
from entoderm. It is not until the time when the blastopore is nearly 
closed that a differentiation of cells is apparent. Even then we are not 
certain that these cells represent the mesoderm since the marked contrast 
in the staining capacity later disappears. To know precisely when and 
how the mesoderm arises and how it extends in Amia will involve better 
methods of staining than we now possess. 
Tur ARCHENTERON. JUPFFER’S VESICLE AND ADHESIVE ORGANS. 
As the archenteric cavity extends the innermost layer of mes-entoderm 
early is differentiated into a well defined layer which we have called 
hypoblast. This layer, together with the invaginated dorsal ectoblast, 
forms the dorsal wall of the archenteron. At the same time there is dif- 
ferentiated a superficial yolk layer which forms the ventral wall of the 
archenteron. The extent of this primitive gut, however, does not corre- 
spond to the extent of the embryo. There is formed both an appendicular 
(Salensky) or post-annal gut and a precephalic gut. Since the changes 
in the posterior portion precede those in the anterior they will be con- 
sidered first. 
It should be remarked here that the closure of the blastopore is com- 
plete, no portion persisting to form the anus. Its line of closure is in- 
