1256 
Zoology. — “On the relation of the anus to the blastopore and on 
the origin of the tail in vertebrates’. By Dr. H. C. Densman.. 
(Communicated by Prof. J. Boeke). 
(Communicated in the meeting of Feb. 24, 1917). 
Both the foregoing communications (May 27 and November 25, 
1916) being mainly dedicated to the mode of contraction of the 
blastopore border of amphibians, in this third one I should like to 
give some facts and considerations concerning the ultimate fate of 
the blastopore and its relation to the anus. 
The statements made by the numerous investigators on this subject 
are so divergent that it must be very difficult for any one who cannot 
judge from personal experience to form a sound opinion. I will try 
to show that the application of the principles of my theory on the 
origin of vertebrates will once more serve to furnish us with the 
solution of an old problem which — especially by GROBBEN’s (1900) 
classification of the animal kingdom — has been resuscitated. 
In the first place the different views and results of former investi- 
gators may be very briefly reviewed. We will confine ourselves 
mainly to the amphibian egg, in which a relation between anus and 
blastopore was for the first time noticed. Anurans and Urodelans will 
be treated separately, because, as I can confirm from my own investi- 
gations on Rana esculenta and Ainblystoma tiyrinum, these two 
groups in the relation of the anus to the blastopore exhibit a notable 
difference. We will begin with that group, on which the first obser- 
vations were made, the Anurans. 
Barrour (1881) in his Text-book gives a description of the origin 
of the anus, based mainly on the figures of Gorrrr (1875) for 
Bombinator igneus and his own investigations on Hana temporaria, 
where the anus breaks through somewhat earlier than appears to 
be the case in toads generally. The blastopore passes into the 
neurenterie canal and the anus eventually arises at the bottom of 
a diverticulum of the alimentary tract, which meets an invagination 
of the skin. Perforation according to Gorrrr’s well-known represen- 
tation 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. 
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 first conclusion is shared 
