132 
between the two is, when measured dorsally, perhaps 
somewhat shorter than when measured ventrally, but the 
difference is very insignificant and we may safely say that the 
length of the dorsal embryonic rudiment is 180°. Although 
in yolk-laden eggs this arch has a somewhat smaller length, 
still the above relation occurs regularly in various animal 
groups. Besides in Amphibia, we find it e.g. in Teleostei; 
especially in those with pelagic eggs not too 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. Also in the anchovy, as we have seen above, this is 
the case. Far ‘from a fundamental difference, as MORGAN 
(1894) thought, we find a fundamental agreement in the 
position of the embryo in Amphibian and Teleostean eggs. Also 
for Amphioxus the same holds good. CERFONTAINE's (1906) 
pictures of gastrulas of Amphioxus with the polar body 
still attached to them show that here also the blastopore 
after having contracted lies approximately diametrically 
opposite the animal pole, while the dorsal blastopore lip ís 
as well formed here near the egg equator. 
We clearly see from fig. 356 that the place of the first 
appearance of the blastoporic rim lies in about the middle 
of the length of the embryo, that consequently the embryo 
is formed half on the black, half on the white surface of 
the egg after the latter has been overgrown by the dorsal 
blastopore lip, 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 *) 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 
