264
L. GALLIEN
single individual. The colored indicators show that there is no migration
of tissues between the two individuals, no replacement of one individual
by the other, no exchange of tissues (Fig. 2). The following combinations
result from the operation :
Asexual H. fusca X d* H. fusca
Asexual H. fusca X 9 H. fusca
If the chimeric individuals are kept at 8°C, gametogenesis is established.
The commencement of gametogenesis affects the normal individual first,
then spreads progressively along the asexual surface, by contact with the
contiguous walls. All the asexual H. fusca associated with a 9 H. fusca
undergo oogenesis (Fig. 3). All the asexual H. fusca associated with a
C? H. fusca undergo spermatogenesis. Thus gametogenesis in asexual hydra
is developed as a sort of contamination. The nature of the sex induced in
FIG. 3. View of the enlarged gonads in a parabiotic pair of an asexual Hydra fusca
(H.As.) and a female Hydra fusca (H. 9 ) maintained at 8°C. Oogenesis has spread
across to the asexual hydra. (After Brien.)
the asexual individual is imposed by that of the normal hydra. It takes
place as if a sexualizing substance were passing from the normal to the
asexual individual. The interstitial cells, in becoming germ cells, are sexually
bivalent. The induction of gametes occurs only in regions of the body
column that are capable of participating in gametogenesis. If the individuals
are only partially joined, and if the union is located just below the hypostome in an area that is not involved in gametogenesis, the sexualizing
induction does not take place in the asexual individual (Fig. 4).
L. GALLIEN
single individual. The colored indicators show that there is no migration
of tissues between the two individuals, no replacement of one individual
by the other, no exchange of tissues (Fig. 2). The following combinations
result from the operation :
Asexual H. fusca X d* H. fusca
Asexual H. fusca X 9 H. fusca
If the chimeric individuals are kept at 8°C, gametogenesis is established.
The commencement of gametogenesis affects the normal individual first,
then spreads progressively along the asexual surface, by contact with the
contiguous walls. All the asexual H. fusca associated with a 9 H. fusca
undergo oogenesis (Fig. 3). All the asexual H. fusca associated with a
C? H. fusca undergo spermatogenesis. Thus gametogenesis in asexual hydra
is developed as a sort of contamination. The nature of the sex induced in
FIG. 3. View of the enlarged gonads in a parabiotic pair of an asexual Hydra fusca
(H.As.) and a female Hydra fusca (H. 9 ) maintained at 8°C. Oogenesis has spread
across to the asexual hydra. (After Brien.)
the asexual individual is imposed by that of the normal hydra. It takes
place as if a sexualizing substance were passing from the normal to the
asexual individual. The interstitial cells, in becoming germ cells, are sexually
bivalent. The induction of gametes occurs only in regions of the body
column that are capable of participating in gametogenesis. If the individuals
are only partially joined, and if the union is located just below the hypostome in an area that is not involved in gametogenesis, the sexualizing
induction does not take place in the asexual individual (Fig. 4).