558
E T I E N N E W O L F F
st. m
6
p
St. IV"
FIG. 13. Experiments on the regional induction of different sections of the head process,
acting on indifferent ectoderm. The results of the experiments are expressed in capital
letters: F, Fore-brain; M , mid-brain; H, hind-brain; S, spinal cord. The small squares
indicate the positions of tissues removed as inducers in each experiment and regrafted under
presumptive ectoderm, f, Prechordal mesoderm; a, p, anterior and posterior parts of head
process. (After Hara, 1961.)
situated on the mid-line and it separates a part of the chord already on
the path of differentiation from undifferentiated mesodermal rudiments
(Fig. 14). In fact, if this region is removed, the backward development
of the chord ceases, but the somites are not affected. Similarly, it would
appear that two somitic organizing centres, of similar properties with
C
d
b
a
E T I E N N E W O L F F
st. m
6
p
St. IV"
FIG. 13. Experiments on the regional induction of different sections of the head process,
acting on indifferent ectoderm. The results of the experiments are expressed in capital
letters: F, Fore-brain; M , mid-brain; H, hind-brain; S, spinal cord. The small squares
indicate the positions of tissues removed as inducers in each experiment and regrafted under
presumptive ectoderm, f, Prechordal mesoderm; a, p, anterior and posterior parts of head
process. (After Hara, 1961.)
situated on the mid-line and it separates a part of the chord already on
the path of differentiation from undifferentiated mesodermal rudiments
(Fig. 14). In fact, if this region is removed, the backward development
of the chord ceases, but the somites are not affected. Similarly, it would
appear that two somitic organizing centres, of similar properties with
C
d
b
a