"^'iSi!^,i:t" ^MMm in the Uni.

186
MOLLUSCOIDA.
tract, the sexual organs, and the vascular system, and is called
" abdominal gem " (Bauchknospe). From the peduncle of the first
come the oesophagus and the rectum. In Botryllus also the egg
produces only one embryo and one individual. The supposed
eight embryos in the egg are the first elements of the stolons, which
augment afterwards in number, and persist in the compound
colony. The other individuals of Botryllus arise from gems produced
by the first. This first individual is always without sexual
organs, and produces, therefore, no eggs; the following individuals,
produced by gemmation, produce eggs. There are no
preexisting orifices for the issue of the eggs; but these force their
way through the integument of the mother, taking a part of it
with them as a temporary envelope.
The first appearance and development of the medullary
tube, the intestinal tract, the branchial sac and its fissures
are the same in the compound and in the simple Ascidians;
but several of Kowalewsky's observations concerning this development
of the embryo are erroneous. Z. wiss. Zool. xx.
pp. 512-518.
Botryllus schlosseri (Pall), Gould, Iuvert. Mass. p. 3, pi. 23. fig. 319, Massachusetts.
POLYZOA.
K. B. REICHERT thinks that in the Bryozoa neither true
muscles nor true nerves exist, the histological structure of the
organs hitherto regarded as such being different from that of the
muscles and nerves of the higher animals ; consequently he proposes
to remove the Bryozoa from the Molluscoida, and to place
them near the Anthozoa and Medusa? in a large division of lower
evertebrate animals, which corresponds otherwise to Leuckart's
Cwleulerata. He regards the Bryozoa generally as subject to
alternating generation—the so-called cell being a distinct previous
individual, to be compared with the " nutrix " of the other
cases of alternating generation, the "collare setosum" (operculum)
and " collare stellatum " belonging to the same, and the
intestinal tractus, with the crown of tentacles, constituting a
second individual, which takes its origin by gemmation from the
first. He adopts for the first the name fostering capsule (Brutkapsel),
for the second the name bryozoid. The whole organization
of the Bryozoa is interpreted according to this view; and
the invagination of the bryozoid within the cell by two sorts of
retractores is the object of special research. Finally, the author
distinguishes between those Bryozoa in which a distinct common
stem exists, called bryozophylon, which bears the single animals
on its sides, as in the Vesiculariadae, and those which are constituted
only by the single animals budding one from the other,
without a common stem, as in most other Bryozoa. He calls