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dorsally, somewhat shorter than when measured ventrally. Hence 
the length of the dorsal embryonic rudiment is a little less than 180°. 
Although in yolk-laden eggs this arch has a somewhat smaller length, 
still the above relation seems to occur regularly in various animal 
groups. For besides in Amphibia we also find it in Teleostei, especially 
in those with pelagic eggs not too much yolk-laden it is generally 
observed that the closure of the blastopore takes place almost 
diametrically opposite the animal pole, i.e. the point of the nose, 
so that here also the embryo extends over almost 180° between 
the animal and vegetative poles. Far from a fundamental difference, 
as Morean (1894) thought, we find a fundamental agreement in the 
position of the embryo in amphibian and teleostean. Also for Amphi- 
oxus the same holds, CERFONTAINE’s (1906) pictures of gastrulas of 
Amphioxus with the second polar body still attached to it, show that 
here too the final narrowed blastopore lies approximately dia- 
metrically opposite the animal pole, while the dorsal blastopore 
lip is equally formed here near the egg equator. 
We clearly see from fig. 2 that the place of the first appearance 
of the blastoporic rim lies about halfway the length of the embryo, 
that consequently the embryo is formed half on the black, half on 
the white hemisphere, and that the main axis of the egg coincides with 
the longitudinal axis of the embryo, so that the second cleavage of 
the egg in so-called typical development (Roux, see later) separates 
the dorsal and ventral halves. Since in the 4- or 8-celled stage the 
distance from the animal to the vegetative pole (upper and lower 
crossing point of the first two cleavage planes) is also a little shorter 
when measured dorsally than when measured ventrally (the two 
ventral cells in stage 4 being somewhat larger than the two dorsal 
ones), it follows as well that the closure of the blastopore takes place 
exactly at the vegetative pole. 
Let us now consider the eggs marked at h, c, or d, which are 
the points of intersection on the third or equatorial cleavage furrow, 
Since the roof of the cleavage cavity is getting continually thinner 
during the processes of cleavage and gastrulation, one would suppose 
that here an extension of surface takes place and that consequently 
the points 5, c, and d move away from each other and from the 
animal pole. To my surprise however | found that, if this be the 
case, still it is to such a small extent that practically the little marks 
remain stationary. This wants explaining. It may be e.g. that the 
volume of the cells decreases by expulsion of liquid into the cleavage 
cavity, or by consumption of yolk by the eell-division which is 
particularly active here, or by both causes. Next year I hope to be 
