SOME ASPECTS OF T H E BIOLOGY O F T H E CHAETOGNATHS
343
understand this, it is sufficient to recall the relative dimensions of the
eggs of Spadella (diameter ca 2 5 0 p ) and the way they pass t o the
exterior. The consequence of this is that even in the best preparations
it is practically always impossible, at the moment of spawning, to
recognize the original topographic relations between the cellular
elements forming the vagina.
The eggs are deposited in clusters of from four t o eight to twelve,
each of which is attached to submerged bodies: in nature t o the
leaves of Zosteracea or seaweeds on which they usually live. Under
experimental conditions, the eggs are attached instead t o the
walls of finger-bowls t o which they adhere by means of an elastic
peduncle.
Vasiljev assumed that Spadella laid their eggs only at night, while
I have been able to observe that, in the laboratory at least, the eggs
can be laid at any time of day-though with a marked preference for
night hours. As far as the other genera of chaetognaths which we have
mentioned in this work are concerned, we lack any observations about
the laying of their eggs. Sanzo (1937) described the eggs of Pterosagitta
draco, which have a very thin shell and are gathered in gelatinous
oothecae which are to be found at different depths according to the
stage of development. Eukrohnia hamata Mobius, which lives in very
cold waters, retains, on the other hand, its few eggs by its lateral fins,
which bend to form a sort of incubation pouch (MacGinitie, 1955;
David, 1955). The eggs of Krohnitta are also gathered by a gelatinous
adhesive secretion in packets that the animal carries for some time
attached near the septum dividing the trunk from the tail (Kuhl,
1928). According to Conant (1896) the eggs of Sagitta hispida are coated
by a jelly which forms in the oviduct in 20-30 min. Each ootheca
contains about sixty or seventy eggs.
F. Habitat and cycles of sexual maturity
Many authors have reported on the influence of environmental
factors on the distribution of the chaetognaths. I shall limit myself
to quoting only Baldasseroni (1914)) Teodoro (1923), Russell (1932a,b,
1933, 1935, 1939), Furnestin, J. (1938), Furnestin, M. L. (1965), Thiel
(1938), Pierce (194l), Gamulin (1948), Tokioka (1952), Bogorov and
Vinogradov (1955), David (1955, 1958b), MacGinitie (1955), Tchindonova (1955), Bieri (1959), Fraser (1962), VuEeti6 (1963), Ghirardelli
(1953b, 1959c, 1962), Hirota (1959, 1961), Murakami (1959), Cannicci
(1959) and Alvarifio (1967b).
I n general, there is a close relationship between the distribution of
the chaetognaths and salinity and temperature, so that chaetognaths
A.M.B.-6
12
343
understand this, it is sufficient to recall the relative dimensions of the
eggs of Spadella (diameter ca 2 5 0 p ) and the way they pass t o the
exterior. The consequence of this is that even in the best preparations
it is practically always impossible, at the moment of spawning, to
recognize the original topographic relations between the cellular
elements forming the vagina.
The eggs are deposited in clusters of from four t o eight to twelve,
each of which is attached to submerged bodies: in nature t o the
leaves of Zosteracea or seaweeds on which they usually live. Under
experimental conditions, the eggs are attached instead t o the
walls of finger-bowls t o which they adhere by means of an elastic
peduncle.
Vasiljev assumed that Spadella laid their eggs only at night, while
I have been able to observe that, in the laboratory at least, the eggs
can be laid at any time of day-though with a marked preference for
night hours. As far as the other genera of chaetognaths which we have
mentioned in this work are concerned, we lack any observations about
the laying of their eggs. Sanzo (1937) described the eggs of Pterosagitta
draco, which have a very thin shell and are gathered in gelatinous
oothecae which are to be found at different depths according to the
stage of development. Eukrohnia hamata Mobius, which lives in very
cold waters, retains, on the other hand, its few eggs by its lateral fins,
which bend to form a sort of incubation pouch (MacGinitie, 1955;
David, 1955). The eggs of Krohnitta are also gathered by a gelatinous
adhesive secretion in packets that the animal carries for some time
attached near the septum dividing the trunk from the tail (Kuhl,
1928). According to Conant (1896) the eggs of Sagitta hispida are coated
by a jelly which forms in the oviduct in 20-30 min. Each ootheca
contains about sixty or seventy eggs.
F. Habitat and cycles of sexual maturity
Many authors have reported on the influence of environmental
factors on the distribution of the chaetognaths. I shall limit myself
to quoting only Baldasseroni (1914)) Teodoro (1923), Russell (1932a,b,
1933, 1935, 1939), Furnestin, J. (1938), Furnestin, M. L. (1965), Thiel
(1938), Pierce (194l), Gamulin (1948), Tokioka (1952), Bogorov and
Vinogradov (1955), David (1955, 1958b), MacGinitie (1955), Tchindonova (1955), Bieri (1959), Fraser (1962), VuEeti6 (1963), Ghirardelli
(1953b, 1959c, 1962), Hirota (1959, 1961), Murakami (1959), Cannicci
(1959) and Alvarifio (1967b).
I n general, there is a close relationship between the distribution of
the chaetognaths and salinity and temperature, so that chaetognaths
A.M.B.-6
12