SOME ASPECTS OF T H E BIOLOGY O F T H E CHAETOGNATHS
327
caudal sephum and even perhaps reaching the orifices of the receptacles.
The majority, however, migrate towards the caudal fin ; the sperms
form here a more or less compact clump after which they generally fall
from the body. I n some instances, a sharp contraction of the tail may
throw the spermatozoa forward toward the caudal septum, but these
too generally detach themselves from the body after a longer or shorter
period: only very few enter the seminal receptacles. The same thing
occurs with spermatozoa which leave the seminal vesicles owing to some
traumatic damage. I n this case, furthermore, the spermatozoa show
that they are unable to climb up the tail.
It is interesting t o note that if one spermatophore is placed on the
neck and at the same time another is put on the tail of a specimen, the
spermatozoa migrate regularly from the spermatophore on the neck,
while those on the tail show the irregular behaviour we have described
above. Spermatophores placed on the ventral region of the body, before
or behind the caudal ganglion, dissolve more or less regularly: the
sperms migrate to the sides of the body heading towards the anal
orifice near which they mass. After a short time they part from the
body and do not seem to be able t o head towards the lateral-dorsal
region of the body where the orifices of the receptacles are situated.
All the foregoing refers t o animals whose epidermis is in perfect
condition. I n the orifices of a specimen whose receptacula seminalis had
been damaged and on whose neck a spermatophore had been placed,
migration occurred speedily but no division took place at the usual
point : the sperms having passed the caudal septum arrived at the tail,
from whence the direction of the migration was reversed and almost
all spermatozoa returned to the neck. Some of them took up position
on the ciliary loop, some passed the loop and took up places at irregular
intervals on the head. The migration of the sperms in the two directions
took about half an hour on the whole. Some hours after the beginning
of the experiment, numerous sperms could still be seen on the head.
If the spermatophore is placed in the centre of the ciliary loop, the
sperms tend t o migrate on t o the head or t o settle on the corona itself:
no migration towards the septum can be observed. If the spermatophore in beheaded specimens, deprived also of the corona ciliata, is
placed on the neck shortly after the operation, the migration occurs
almost always and it is regular enough. One hour after the cutting,
however, the spermatozoa either migrate no more or do so in a completely irregular manner.
These observations should then allow one to conclude that in
Xpadella cephaloptera fertilization occurs following a reciprocal mating,
though it is possible, as we have seen, t o obtain self-fertilization
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caudal sephum and even perhaps reaching the orifices of the receptacles.
The majority, however, migrate towards the caudal fin ; the sperms
form here a more or less compact clump after which they generally fall
from the body. I n some instances, a sharp contraction of the tail may
throw the spermatozoa forward toward the caudal septum, but these
too generally detach themselves from the body after a longer or shorter
period: only very few enter the seminal receptacles. The same thing
occurs with spermatozoa which leave the seminal vesicles owing to some
traumatic damage. I n this case, furthermore, the spermatozoa show
that they are unable to climb up the tail.
It is interesting t o note that if one spermatophore is placed on the
neck and at the same time another is put on the tail of a specimen, the
spermatozoa migrate regularly from the spermatophore on the neck,
while those on the tail show the irregular behaviour we have described
above. Spermatophores placed on the ventral region of the body, before
or behind the caudal ganglion, dissolve more or less regularly: the
sperms migrate to the sides of the body heading towards the anal
orifice near which they mass. After a short time they part from the
body and do not seem to be able t o head towards the lateral-dorsal
region of the body where the orifices of the receptacles are situated.
All the foregoing refers t o animals whose epidermis is in perfect
condition. I n the orifices of a specimen whose receptacula seminalis had
been damaged and on whose neck a spermatophore had been placed,
migration occurred speedily but no division took place at the usual
point : the sperms having passed the caudal septum arrived at the tail,
from whence the direction of the migration was reversed and almost
all spermatozoa returned to the neck. Some of them took up position
on the ciliary loop, some passed the loop and took up places at irregular
intervals on the head. The migration of the sperms in the two directions
took about half an hour on the whole. Some hours after the beginning
of the experiment, numerous sperms could still be seen on the head.
If the spermatophore is placed in the centre of the ciliary loop, the
sperms tend t o migrate on t o the head or t o settle on the corona itself:
no migration towards the septum can be observed. If the spermatophore in beheaded specimens, deprived also of the corona ciliata, is
placed on the neck shortly after the operation, the migration occurs
almost always and it is regular enough. One hour after the cutting,
however, the spermatozoa either migrate no more or do so in a completely irregular manner.
These observations should then allow one to conclude that in
Xpadella cephaloptera fertilization occurs following a reciprocal mating,
though it is possible, as we have seen, t o obtain self-fertilization