580 The American Naturalist. [July, 
EXPERIMENTAL EMBRYOLOGY. 
By E. A. ANDREWS. 
(Continued from May number, p. 382.) 
Schultze’ holds that the black pole becomes the dorsal region 
on which the medullary folds are formed, and that the blasto- 
pore arises and remains near the tail end of the animal, at the 
highest part of the white yolk, when the egg is, as is normal 
he says, inclined about 45°. There is, however, a rotation of 
the egg about a horizontal axis at right angles tothe plane of 
symmetry, a rotation that carries blastopore downward 80°. 
Yet this is compensated for by a reverse rotation upward of 
90°, so that there is little absolute change after the blastopore 
is closed ; the ingrowth of entoderm during gastrulation being, 
he surmises, the cause of these revolutions, since the egg is 
thereby overbalanced, first one way then thé other. 
After this digression beyond the limits of experimental 
embryology into the hazy ground of unverified hypotheses we 
may turn attention to a work rich in experimentation, the only 
French contribution that we are acquainted with, the very 
suggestive work upon the ascidian egg by Chabry, whose 
paper appears not to have met with the appreciation it 
deserves. 
Having made a very careful study of the cleavage phenom- 
ena in normal eggs of Ascidia aspera in the summer seasons — 
of 1884 and 1886, the author was in a position to appreciate 
the remarkable abnormalities sometimes occurring in the a 
development of this ascidian. As these abnormalities to some 
extent correspond with the results of artificial treatment of a | 
the eggs, some account of them cannot be passed over here, 
10. Schultze, Ueber Axenbestimmung des Froshembryo. Biol. Centb., vii, 1888, 
pp- 577-588. 
*Contribution a l’embryologie normale et tératologique des ascidies simples. Jour. 
de l’ Anatomie, 1887, pp. 167-313, plates 18-22. 
