50 
HAROLD SIDEBOTHAM. 
In a paper 1 “On some Points in the Early Development of 
Uana temp or aria” Professor Spencer states that he is unable 
to find any trace of the inclusion of the blastopore by the 
neural folds, or any trace of the closure of the blastopore itself. 
He also states that soon after the stage has been reached in 
which the neural folds have met, the hinder part of the neural 
tube becomes closed, though the blastopore itself remains 
open. 
Miss Johnson and Miss Sheldon have also published some 
“Notes on the Development of the Newt,” 2 in which they 
make some remarks with regard to the Frog. They apparently 
agree with Professor Spencer in the opinion that the blastopore 
persists as the permanent anus. 
Mr. Herbert Durham 3 has also stated that he fully agrees 
with Professor Spencer in regard to the fate of the blastopore. 
Being interested in this question I have cut a large number of 
series of sections of Rana temporaria. A careful study of 
these sections leads me to come forward and express my 
opinion, and that with some degree of confidence, as more than 
sixty embryos have been examined, that the history of the 
blastopore more resembles the account of it given by Balfour 
than that given by any of the other authors above alluded to. 
After the formation of the neural folds, and while they are 
still widely separated, the mesenteron opens to the exterior by 
means of the blastopore, which is situated at the extreme 
posterior end of the embryo. Fig. 1 shows a median, vertical, 
longitudinal section, taken at this stage ; in it can be seen a 
well-marked diverticulum from the hind end of the mesen- 
teron, dipping down towards a distinct pit in the epiblast 
below the blastopore and quite separate from it. This is the 
rectum forming, and advancing to meet a true proctodseal pit. 
This embryo has three mesoblastic somites. As the neural 
folds grow up to meet each other they do not enclose the blas- 
topore, but reach as far as its dorsal rim. 
1 ‘Quart,. Journ. Micr. Sci.,’ vol. xxv, Supplement, 1885, p. 123. 
2 ‘Quart. Journ. Micr. Sci.,’ vol. xxvi, 1886, p. 573. 
3 ‘Quart. Journ. Micr. Sci.,’ vol. xxvi, 1886, p. 508. 
