tell
before examination under the compound microscope, whether or not I
should see spermatozoa. Many had distinct heads,[52] which were two or
three times as broad as the filamentary bodies; the latter when placed
between glass were the 1/20,000th of an inch in diameter. I compared
these spermatozoa with others taken out of the vesiculae seminales of the
individual hermaphrodite _S. vulgare_, to which the parasite was
attached, and could not perceive the slightest difference in them. The
brownish pear-shaped bag, or vesicula seminalis, the coat of which seems
fibrous, could sometimes be distinctly traced, sending a chord or
prolongation far up the thorax: at the end of the abdominal lobe, no
doubt there is an orifice; and this, I believe, I once distinguished.
Owing to this chord, the bag often adheres to the thorax, when the
latter is dissected out of the general integuments; in this condition, I
twice clearly made out that it was single: in one other specimen,
however, there appeared to be two small vesiculae seminales. By using a
condenser and very brilliant light, the outline of the vesicula
seminalis could sometimes be distinguished before dissection, at the
bottom of the sack-formed animal; and such was the case in the specimen
drawn in fig. 9.

[52] I do not understand the development of the spermatozoa in
Cirripedia: in a recent Chthamalus and Balanus, I found the
greater number had a little filament in front of the head or
nodular enlargement, which latter varied in size and in shape
from globular to that of a spindle. The filament before the head,
also, varied in proportional length; it did not project in
exactly the same straight line with the hinder part, and some of
the spermatozoa were entirely without this filament in
front;--such is the case with the spermatozoa here described.

Although I have dissected, at least, thirty specimens, taken at
different times of the year, and from different localities, and when
many of the specimens were mature and ready for the impregnation of ova,
as clearly shown by the presence of innumerable spermatozoa, I have
never seen even a trace of an ovum or ovaria.

_Antennae and Attachment._--The prehensile antennae (Pl. V, fig. 10), are
seated a little above the very base of the sack-like animal; and this
might have been expected from the antennae in the larva, being seated on
the ventral surface, not at the very extremity of the head. By a very