1890.] The Mesoderm and the Catlom. 881 
derm in the axial line above the notochord; at the edge of the 
notochord, where it joins the undifferentiated epithelial ento- 
derm of the archenteron, there is on each side a groove 
which in cross sections appears as a notch (Fig. 23); the 
notch is of variable depth, is sometimes absent, and is a tempor- 
ary feature. In the neighborhood of the furrow, alongside the 
notochord, the mesoderm is still intimately connected with the 
entoderm. These relations are believed by Hertwig to indicate 
that the mesoderm arises as two masses, which is not the case, 
and that each mass is really a diverticulum of the archenteron, the 
furrow being the mouth of the diverticular cavity. Hertwig’s 
figures, r2, Taf. x111.—xIVv., offer the plainest representations of 
the mesoderm in Triton as paired diverticula; but these figures ? 
are evidently digramatic, and they must be termed inaccurate, I 
think, in the very respect which are essential to Hertwig's 
theory. This appears from the investigations of Gotte, zo, Bel- 
lonci, 5, Bambeke, 5, O. Schultze, 35, and others; compare also 
K. Lampert, 27. The reader may compare, for instance, Hert- 
wig's Fig. 10, Zc. Taf. xir, with Bellonci’s Fig. 11, Ze. Tav. m1. 
O. Schultze's detailed criticism, /.c. 344—349, of Hertwig's account 
seems to me entirely justified, and I accordingly accept it as a 
complete disproof This criticism shows that Hertwig's concep- 
tion is based upon insufficient and erroneous observations; insuffi- 
cient because he did not investigate the early condition of the 
mesoderm, and failed to recognize the fugitive and unessential 
character of parachordal grooves; erroneous because the cavity 
in the mesoderm does not really communicate with that of the 
archenteron. There are other errors, which Schultze points out, 
and which are important. 
We find in amphibia, at a certain stage, the axial (Rabl's gas- 
trales) and lateral (Rabl’s peristomales) mesoderm. The former 
is in the region of the completed concrescence, the latter around 
the edge of the anus of Rusconi. The former is connected with 
the entoderm alone; the latter with the ectoderm also, since the 
entoderm is connected with the ectoderm around the uncon- 
? Some of them are reproduced in Hertwig's Lehrbuch der Entwickelungsgeschichte, 
sechstes Capitel. 
