SOME ASPECTS O F THE BIOLOGY O F THE CHAETOGNATIIS
35 1
IV. REGENERATION
Only a limited number of experiments have been done on regeneration in chaetognaths. The observations of Kulmatycki (1 918) and
Pierce (1951) attracted my attention, since the conclusions of these
two authors were in my opinion contrary to the general rule that
animals in which there is a precocious determination of the germinal
line do not have high regenerative powers.
I n fact, according to Kulmatycki and Pierce, chaetognaths are gifted
with considerable regenerative powers. Kulmatycki (1 91 8) found that
Xpadella could regenerate the whole caudal section, while in Xugitta,
according to Pierce (1951), there is also regeneration of the head.
As we have said, chaetognaths are animals in which the determination of the germinal line occurs quite early, and in general there are
rather close connexions between regenerative power and the stage at
which the segregation of the germinal line occurs. Organisms with a
precocious determination of the primordial germ cells have usually a
very limited regenerative ability, never sufficient to allow the formation of complete new individuals from a part of the body, and they
cannot regenerate important and large portions of their bodies. They
lack the power of asexual reproduction by fission, by budding, and in
short by all the different methods of blastogenesis (Ghirardelli, 1964d,
195913). By contrast, this power is often quite remarkable in those
groups of animals in which there is no precocious determination of the
germ-cell line, and in which a reserve of totipotential cells persists
throughout their whole life, able to differentiate either into all somatic
cells or into germ-cells.
Now, chaetognaths completely lack the power of asexual reproduction and, even if their relation with other zoological groups is still not
well known, they have been considered to be related to groups nearly
devoid of regenerative power, as for instance the nematodes (see
p. 356). All this suggested that the regenerative ability of the chaetognaths could not be as good as stated by Kulmatycki and Pierce.
Therefore I have repeat,ed in Xpadella cephaloptera, with few modifications, Kulmatycki’s experiments and I have made some observations
on material analogous to that described by Pierce, i.e. beheaded Xagitta
inJEata and Xagitta sp. collected in plankton samples at Villefranche and
in the north Adriatic. Operations carried out upon Spndella are shown
in Fig. 34; the cuts marked with the numbers 1-6 are the same as
Kulmatycki’s, the cuts 7 and S correspond to new operations.
The regeneration of the caudal fin is always very rapid (from 2 to 4
days), provided that the posterior part of the body proper has not been
12’
35 1
IV. REGENERATION
Only a limited number of experiments have been done on regeneration in chaetognaths. The observations of Kulmatycki (1 918) and
Pierce (1951) attracted my attention, since the conclusions of these
two authors were in my opinion contrary to the general rule that
animals in which there is a precocious determination of the germinal
line do not have high regenerative powers.
I n fact, according to Kulmatycki and Pierce, chaetognaths are gifted
with considerable regenerative powers. Kulmatycki (1 91 8) found that
Xpadella could regenerate the whole caudal section, while in Xugitta,
according to Pierce (1951), there is also regeneration of the head.
As we have said, chaetognaths are animals in which the determination of the germinal line occurs quite early, and in general there are
rather close connexions between regenerative power and the stage at
which the segregation of the germinal line occurs. Organisms with a
precocious determination of the primordial germ cells have usually a
very limited regenerative ability, never sufficient to allow the formation of complete new individuals from a part of the body, and they
cannot regenerate important and large portions of their bodies. They
lack the power of asexual reproduction by fission, by budding, and in
short by all the different methods of blastogenesis (Ghirardelli, 1964d,
195913). By contrast, this power is often quite remarkable in those
groups of animals in which there is no precocious determination of the
germ-cell line, and in which a reserve of totipotential cells persists
throughout their whole life, able to differentiate either into all somatic
cells or into germ-cells.
Now, chaetognaths completely lack the power of asexual reproduction and, even if their relation with other zoological groups is still not
well known, they have been considered to be related to groups nearly
devoid of regenerative power, as for instance the nematodes (see
p. 356). All this suggested that the regenerative ability of the chaetognaths could not be as good as stated by Kulmatycki and Pierce.
Therefore I have repeat,ed in Xpadella cephaloptera, with few modifications, Kulmatycki’s experiments and I have made some observations
on material analogous to that described by Pierce, i.e. beheaded Xagitta
inJEata and Xagitta sp. collected in plankton samples at Villefranche and
in the north Adriatic. Operations carried out upon Spndella are shown
in Fig. 34; the cuts marked with the numbers 1-6 are the same as
Kulmatycki’s, the cuts 7 and S correspond to new operations.
The regeneration of the caudal fin is always very rapid (from 2 to 4
days), provided that the posterior part of the body proper has not been
12’