section 
Fig. 1. Three eggs of Rana esculenta during the closure of the medullary folds 
(a) anal pit. Jl. blastopore. 
similar longitudinal series one succeeds better than might be expected 
in getting the blastopore as an opening (bl), though of course this 
is only the case in one or two sections. The ventral blastopore lip 
is well developed and includes between itself and the yolkmass in 
the archenteron the anal diverticulum (Afterdarm, a.d.), which 
however is nothing but the intersection of a circular incision 
surrounding the mass of yolk-cells. 
In a somewhat further advanced stage appears on the surface of 
the egg (textfig. 16) behind the slit-like blastopore a shallow 
impression in the ectoderm (a), also clearly visible in a longitudinal 
section, as in fig. 2 of the plate. Underneath this impression a 
thickening of the ectoderm occurs, of which the beginning is already 
visible in fig. 1 (%). Opposite the invagination of the ectoderm a 
similar one is found in the entoderm at the bottom of the anal 
diverticulum. 
In an egg as represented in textfig. Ic we see at the bottom of 
the shallow invagination of the ectoderm mentioned above a little 
pit, as yet not very deep, from which a still more shallow groove, 
the anal groove, runs forward to the blastopore-slit. The longitudinal 
section of this egg is given in fig. 3 of the plate. It bears a close 
relation to fig. 2, the anal membrane however has become thinner. 
In a slightly further advanced stage, not represented here, the 
greatest part of the slit-like blastopore has been overgrown by the 
medullary folds, only at the hindmost extremity is there still a litlle 
opening, from which the anal groove runs to the anal pit. This 
anal groove, with a deeper depression at its anterior (rest blastopore) 
and at its posterior end (anal pit) appears to have been confused 
by several authors with the slit-like blastopore of fig. 1a and 4, 
