145 
alimentary tract which meets an invagination of the skin. 
Perforation, according to GOETTE's well-known represent- 
ation of a longitudinal section in Bombinator, only occurs 
when the growth of the tail is well advanced, in Rana 
temporaria according to BALFOUR somewhat earlier. 
HERTWIG (1883, p. 285) also sees the anus in Rana 
temporaria arise behind and independently from the slit- 
like blastopore. He emphasizes the different behaviour of . 
the germinal layers at the border of the two structures. 
At the blastopore border ecto- and entoderm are continuous 
with the mesoblast and are separated from each other by the 
latter. At the anus, on the contrary, ecto- and entoderm 
pass directly into each other, forming a passage which 
pierces the mesoderm at that place. 
SPENCER (1885), on the contrary, comes to the conclusion 
that" the blastopore in Rana temporaria remains open and 
passes directly into the anus The blastopore is not enclosed 
by the medullary folds and thus there is no neurenteric 
canal. The former conclusion is shared by DURHAM (1886) 
in a short note, but according to the latter, a neurenteric 
canal is formed independently from the blastopore. In 
one series, truly, DURHAM finds no blastoporal opening 
whatever but considers this as a pathological case KUPFFER 
(1887), dealing with the same object, comes to the conclu- 
sion that the blastopore remains open as the anus; so, also 
PERENYI (1888). 
SCHANZ (1887) also operated on Rana temporaria, together 
with Friton. In Rana he concludes that the medullary 
folds rather close over the blastopore, that there is indeed 
a neurenteric canal, though the lumen is not evident, and 
that the anus arises by perforation at the bottom of a little 
groove behind it. 
As regards the facts SIDEBOTHAM (1888) quite agrees 
with him. According to him BALFOUR's description is the 
right one, he too sees in sections the “diverticulum from 
the hind end of the mesenteron, dipping down towards 
a distinct pit in the epiblast below the blastopore and 
uite separate from it” Eventually perforation ensues. 
Similarly by MORGAN (1890) in Rana halecina and Bufo 
lentiginosus the anus is seen to arise at the bottom of a 
little groove in the ectoderm behind the blastopore. 
GOETTE (1890), after a renewed investigation on Bom- 
binator igneus and some other Anurans reaches the con- 
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