382
JEAN J. PASTEELS
different directions : in some cases, both dorsal and ventral blastomeres
resulted in more or less complete embryos (in some cases with some
microcephaly) ; in other cases the dorsal blastomere alone would give an
embryo, whereas the ventral one became a
t
Bauchstück' ; but in some
cases also the development of the dorsal piece was inhibited (cf. Fig. 11).
FIG. 12. Separation by aligature of lateral blastomeres in Triton. (L. =left; R. =right)
(a) Before the experiment: the clear crescent has been stained with Nile blue; (b) during
the experiment; (c) the separation being completed; (d) at gastrulation: the planes of
symmetry are shifted laterally. (After Dollander, 1950.)
The conclusions of Spemann could not therefore be confirmed with
regard to the separation of a dorsal and a frontal blastomere by frontal
ligature. We have already pointed out the contradiction between the
formation of a whole embryo from a ventral blastomere, and Curtis' idea
of an 'activation centre' which does not act as a field.
(b) The ligature causes actual stretching of the cortical layers which,
after separation of the blastomeres, may be estimated to amount to a