ANIMALIZATION AND VEGETALIZATION
157
Isolated vegetal halves show only a single gradient of reduction
directed from the vegetal pole to the animal pole (acropetal gradient)
(Fig. 4). The entire eggs, vegetalized by lithium, also present a single
acropetal gradient (Fig. 5).
Isolated animal halves have a single gradient of reduction directed
from the animal pole to the vegetal pole (basipetal gradient) (Fig. 6).
The animalized entire egg also shows a stronger basipetal gradient (Fig. 7).
18,20
18,30
W,40
FIG. 7. Reduction gradients in eggs animalized by trypsin. The animal gradient is
much stronger than the vegetal one (from Hörstadius, 1955).
Eggs animalized by trypsin (Hörstadius, 1955) or by zinc (Lallier, 1956c)
show the same basipetal gradient. The formation of this gradient seems
then directly bound to animalization and is independent of the experimental processes used to obtain it.
The gradients of reduction may be modified by the influence of a
strongly vegetative material, such as the micromeres. For instance,
when micromeres are laterally implanted in the animal zone of the whole
egg, they induce in it the formation of a new centre of reduction.
Moreover, the implantation of 4 micromeres into an isolated animal
half induces in it a new gradient (acropetal gradient) and confines the
pre-existing basipetal gradient inside the animal half. As a result, we
have a system of two gradients comparable with the one of the normal
embryo. Moreover the combination of an animal half with 4 micromeres
is able to develop into a typical pluteus.
In conclusion, modifications of embryonic determination, vegetalization or animalization, disturb the gradient of reduction. These perturbations have opposite signs and are directly bound to animalization and
F
157
Isolated vegetal halves show only a single gradient of reduction
directed from the vegetal pole to the animal pole (acropetal gradient)
(Fig. 4). The entire eggs, vegetalized by lithium, also present a single
acropetal gradient (Fig. 5).
Isolated animal halves have a single gradient of reduction directed
from the animal pole to the vegetal pole (basipetal gradient) (Fig. 6).
The animalized entire egg also shows a stronger basipetal gradient (Fig. 7).
18,20
18,30
W,40
FIG. 7. Reduction gradients in eggs animalized by trypsin. The animal gradient is
much stronger than the vegetal one (from Hörstadius, 1955).
Eggs animalized by trypsin (Hörstadius, 1955) or by zinc (Lallier, 1956c)
show the same basipetal gradient. The formation of this gradient seems
then directly bound to animalization and is independent of the experimental processes used to obtain it.
The gradients of reduction may be modified by the influence of a
strongly vegetative material, such as the micromeres. For instance,
when micromeres are laterally implanted in the animal zone of the whole
egg, they induce in it the formation of a new centre of reduction.
Moreover, the implantation of 4 micromeres into an isolated animal
half induces in it a new gradient (acropetal gradient) and confines the
pre-existing basipetal gradient inside the animal half. As a result, we
have a system of two gradients comparable with the one of the normal
embryo. Moreover the combination of an animal half with 4 micromeres
is able to develop into a typical pluteus.
In conclusion, modifications of embryonic determination, vegetalization or animalization, disturb the gradient of reduction. These perturbations have opposite signs and are directly bound to animalization and
F