
536 THE AMERICAN NATURALIST. [Vor. XXXVI. 
Goette (6), one of the early workers on the development of 
the amphibian egg, considered the mesoderm in the egg of 
Bombinator to arise from the splitting off of a layer of cells 
from the primitive entoblast, the layer thus formed extending 
as an unbroken sheet across the dorsal wall of the archenteron. 
The rest of the primitive entoblast was said to form the endo- 
derm. According to Goette, a central chord of mesoderm in 
the mid-dorsal region of the embryo separates from the two 
lateral sheets to form the notochord. 
A few years later Hertwig (7), after studying the develop- 
ment of the eggs of Triton and of Rana temporaria, came to 
the conclusion that the mesoderm in the amphibian egg arises 
in the vicinity of the blastopore “durch eine paarige Ein- 
faltung des Entoblast schon zu einer Zeit wo die Gastrula- 
einstülpung noch nicht ganz vollendet ist." The amphibian egg 
was thus brought into agreement with Hertwig's observations 
on the development of other vertebrates and gave additional 
support to his well-known ccelom theory. A few other 
writers — Balfour (2), Marshall (14), and Schwink (26)— 
agree with the results obtained by Hertwig. 
In 1888, Schultze (25), from observations on Rana fusca, 
decided that “das mittlere Blatt, sowie die dorsale Urdarm- 
wand entstehen aus dem Ektoblast und gehen an der dorsalen 
Urmundlippe alle drei Blatter in einander iiber; in den seit- 
lichen und ventralen Theilen des Blastoporus setzt sich die 
Deckschicht des áusseren Keimblattes mit besonderer Klarheit 
in den Entoblast, die Grundschicht des Ektoblast ohne Unter- 
brechung in den Mesoblast fort."  Perenyi (18), from obser- 
vations on the egg of Bombinator igneus, Lwoff (13), from a 
study of Axolotl and various Anura, and Brauer (3), from 
investigations on two species of Gymnophiona, also came to 
the conclusion that the mesoderm is ectodermal in origin. 
These investigators, however, differ somewhat regarding the 
manner in which this process is supposed to take place. 
Perenyi states that, as a result of a turning under, or “ Dupli- 
kation," of the three-layered outer wall of the egg at the lips of 
the blastopore, “ die aussersten Deckzellen der Blastula in ihrer 
ununterbrochenen Fortsetzung nach innen endlich die untersten 

