SOME ASPECTS O F THE BIOLOGY O F T H E CHAETOGNATHS
291
Spadella it is always slower than in Sagitta bipunctata and related
species. According to BordAs (1912, 1914) the polyplasts are incompletely separated from each other by the walls and trabeculae of a kind
of net present in the testicular space. Observations in vivo do not,
however, show this testicular net, but histological sections do; it
seems to be due to coagulation and precipitation of the liquids which
fill the cavity of the tail coelom.
Much has been said about the causes of the movements of the
polyplasts. Some workers believe it to be due to the ciliated cells
that cover the median septum (Burfield, 1927) while for BordAs the
movement of the germinal elements is simply due to the tail action of
mature spermatozoa. But this explanation is hardly satisfactory,
since the movement of the spermatocytes can also be seen when adult
spermatozoa are absent. An important part in causing the phenomenon could also be played by the ciliation at the mouth of the vasa
deferentia.
I n order to come out into the open, mature spermatozoa pass
through a thin canal which opens into the caudal coelom by a
ciliated funnel which Goodrich (1945) considered to be a propcr coelomostoma. These ducts run without noteworthy turns or convolutions
within the body wall and open into the front end of the seminal vesicles.
These vesicles have quite different forms according to the spccies and
their degree of fullness and arc situated on the lateral areas of the body
between the ends of the posterior lateral fins and the fore part of the
caudal fin. They are covered by epidermis and their opening shows
some quite peculiar features, particularly evident in Sagittu injata and
S. serratodentata. They are generally structures of a chitinous appearance in the form of a cup, more or less reticulated (8. inflata) or with
finely toothed edges (8. bipunctata and S . serratodentata pac4fica) which
in some species have a systematic value (Kulh, 1938 ; Jagersten, 1940 ;
Thomson, 1947; Tokioka, 1939b, 1942 ; Ghirardelli, 1950a ; Furnestin,
1957) and probably in some pelagic species are for attaching the spcrmatophores to the body during mating (Ghirardelli, 1959c,d). (p. 333).
I n S. injluta one must further remember the differences in the male
reproductive apparatus. In this species, the male germinal elements in
the various stages of maturity are not more or less uniformly diffused in
the whole trunk coelom, but they are confined to two almost ovoidal
areas nearby the tail. This species then shows in the reproductive apparatus some differences from the other species of the
genus Sugitta, which for purposes of classification are perhaps more
important than the differences in the number and disposition of the
fins.
291
Spadella it is always slower than in Sagitta bipunctata and related
species. According to BordAs (1912, 1914) the polyplasts are incompletely separated from each other by the walls and trabeculae of a kind
of net present in the testicular space. Observations in vivo do not,
however, show this testicular net, but histological sections do; it
seems to be due to coagulation and precipitation of the liquids which
fill the cavity of the tail coelom.
Much has been said about the causes of the movements of the
polyplasts. Some workers believe it to be due to the ciliated cells
that cover the median septum (Burfield, 1927) while for BordAs the
movement of the germinal elements is simply due to the tail action of
mature spermatozoa. But this explanation is hardly satisfactory,
since the movement of the spermatocytes can also be seen when adult
spermatozoa are absent. An important part in causing the phenomenon could also be played by the ciliation at the mouth of the vasa
deferentia.
I n order to come out into the open, mature spermatozoa pass
through a thin canal which opens into the caudal coelom by a
ciliated funnel which Goodrich (1945) considered to be a propcr coelomostoma. These ducts run without noteworthy turns or convolutions
within the body wall and open into the front end of the seminal vesicles.
These vesicles have quite different forms according to the spccies and
their degree of fullness and arc situated on the lateral areas of the body
between the ends of the posterior lateral fins and the fore part of the
caudal fin. They are covered by epidermis and their opening shows
some quite peculiar features, particularly evident in Sagittu injata and
S. serratodentata. They are generally structures of a chitinous appearance in the form of a cup, more or less reticulated (8. inflata) or with
finely toothed edges (8. bipunctata and S . serratodentata pac4fica) which
in some species have a systematic value (Kulh, 1938 ; Jagersten, 1940 ;
Thomson, 1947; Tokioka, 1939b, 1942 ; Ghirardelli, 1950a ; Furnestin,
1957) and probably in some pelagic species are for attaching the spcrmatophores to the body during mating (Ghirardelli, 1959c,d). (p. 333).
I n S. injluta one must further remember the differences in the male
reproductive apparatus. In this species, the male germinal elements in
the various stages of maturity are not more or less uniformly diffused in
the whole trunk coelom, but they are confined to two almost ovoidal
areas nearby the tail. This species then shows in the reproductive apparatus some differences from the other species of the
genus Sugitta, which for purposes of classification are perhaps more
important than the differences in the number and disposition of the
fins.