348
ELVEZIO GHIRARDELLI
caudal section (Ghirardelli, 1962). As far as the total lengths are
concerned, the diagrams show a normal distribution, while those
concerning the caudal segment confirm that two groups of individuals
exist, though there is a good connexion between total length and the
length of the caudal section which increases with the increase of the
length of the body: at equal dimensions, however, there is a certain
degree of variability.
I n the Indian Ocean, Rao and Kelly (1962) have observed in S.
injata a variation in size during the year : the maximum length of the
body is coincident with the abundance of copepods. Stone (1966), in
a study of S. inJEata of the Agulhas Current in South Africa, has
observed that the specimens collected in neritic waters contained more
eggs than those from oceanic waters. He postulates that the differences
in the number of eggs per individual, between the two areas, is
advantageous to the species. This adaptation would actually ensure
that the species has sufficient reproductive potential to maintain
populations in the oceanic area, and particularly in the neritic area
which is characterized by a wide range of physical and biological
parameters.
Seasonal variation regarding not only reproduction but also the
corona ciliata and collarette have been observed in S. crassa. First
Tokioka (1940) reported some variations in these characters, and
afterwards Kado and Hirota (1957) and Hirota (1959, 1961) distinguished four classes of S. crassa according t o the form of the collarette :
class A is S. crassa typica, class D is the form naikaiensis and B and C
are intermediate forms. X. crassa in the Sea of Mukaishima has three
alternating main spawning periods, February-March, May-July,
November-December, in which the generation alternates. In the two
generations that the individuals mainly spawn from May to July and
from November to December, the collarette belongs t o class D or C in
low degree. But in the generation which the individuals mainly spawn
from February t o March, the collarette is able to develop in order into
class C, B and A ; the collarette comes into class C from December t o
January, into class B from January to February and into class A in
and after February. The development of the collarette is related to
temperature and salinity. A and B forms are stenohaline and stenothermal (Hirota, 1959, 1961).
X. crassa was accurately studied also by Murakami (1959) in the
field population and in the laboratory, and the results of the rearing
experiments were advantageously used in interpreting the results of the
examination of field samples. I n this manner it was demonstrated that
the forms of the collarette depend on the temperature. Both spawning
ELVEZIO GHIRARDELLI
caudal section (Ghirardelli, 1962). As far as the total lengths are
concerned, the diagrams show a normal distribution, while those
concerning the caudal segment confirm that two groups of individuals
exist, though there is a good connexion between total length and the
length of the caudal section which increases with the increase of the
length of the body: at equal dimensions, however, there is a certain
degree of variability.
I n the Indian Ocean, Rao and Kelly (1962) have observed in S.
injata a variation in size during the year : the maximum length of the
body is coincident with the abundance of copepods. Stone (1966), in
a study of S. inJEata of the Agulhas Current in South Africa, has
observed that the specimens collected in neritic waters contained more
eggs than those from oceanic waters. He postulates that the differences
in the number of eggs per individual, between the two areas, is
advantageous to the species. This adaptation would actually ensure
that the species has sufficient reproductive potential to maintain
populations in the oceanic area, and particularly in the neritic area
which is characterized by a wide range of physical and biological
parameters.
Seasonal variation regarding not only reproduction but also the
corona ciliata and collarette have been observed in S. crassa. First
Tokioka (1940) reported some variations in these characters, and
afterwards Kado and Hirota (1957) and Hirota (1959, 1961) distinguished four classes of S. crassa according t o the form of the collarette :
class A is S. crassa typica, class D is the form naikaiensis and B and C
are intermediate forms. X. crassa in the Sea of Mukaishima has three
alternating main spawning periods, February-March, May-July,
November-December, in which the generation alternates. In the two
generations that the individuals mainly spawn from May to July and
from November to December, the collarette belongs t o class D or C in
low degree. But in the generation which the individuals mainly spawn
from February t o March, the collarette is able to develop in order into
class C, B and A ; the collarette comes into class C from December t o
January, into class B from January to February and into class A in
and after February. The development of the collarette is related to
temperature and salinity. A and B forms are stenohaline and stenothermal (Hirota, 1959, 1961).
X. crassa was accurately studied also by Murakami (1959) in the
field population and in the laboratory, and the results of the rearing
experiments were advantageously used in interpreting the results of the
examination of field samples. I n this manner it was demonstrated that
the forms of the collarette depend on the temperature. Both spawning