92 Moll. 
MOLLUSCOIDA. 
bodies” [see Zool. Rec. viii. p. 179] are, according to him, dead and 
decaying polypids, which sometimes come into the interior of living poly- 
pids, and are then removed by the vent, either as a whole or in pieces. 
The eggs are formed at the tip of the funiculus, the spermatozoids at its 
base ; the funiculus as well as the retractor muscles are to be regarded as 
parts of the polypid ; the eggs pass from thence into peculiar ovicells, 
and are fecundated either before or after their entrance ; the fecundating 
spermatozoids come in most cases from another cystid, the spermato- 
zoids of the same cystids attaining maturity much sooner than the eggs 
[as in many plants]. The cystid produces the polypid by gemmation, 
and the polypid produces the larva by sexual generation. The same 
zooocium (cystid) can produce several polypids in succession, but the first 
are all sterile, and only the last fertile, and after the production of the 
larva, both cystid and polypid perish. The larva passes by meta- 
morphosis into the zooecium ; in Alcyonidium, Sarcochitum, and Pedicel- 
lina, the free larva already contains within itself a body homologous to 
the latter polypid. Arch. Z. exp^r. vi. pp. 193-280, pis. vi.-xiii. Pre- 
liminary notes in 0. R. Ixxxiv. pp. 723-725, and Ixxxv. p. 406. Abstract 
in Ann. N. H. (4) xx. pp. 640 & 541. 
Koren & Danielsen, Faun. litt. Norveg. pt. iii., from observations 
made on some Bugulidce^ also come to the result that no colonial nervous 
system exists in the Pqlyzoa ; they describe a peculiar system of muscles 
in each zooecium, by which, if several individuals are irritated at the 
same moment, the whole branch shows a movement. 
Hatschek, 1. c., opposes the distinction of polypid and cystid as two 
distinct individuals, and urges the homology of the mesoderm and 
tentacles in the different subdivisions of the Polyzoa. The germinal 
strata of the bud are, according to him, throughout originally parts of the 
same strata (ectoderm, mesoderm, or endoderm of the mother) ; the larvae 
of all Cyclostomata agree essentially in their structure with the larvae of 
the Endoprocta, the fringe of cilia surrounding mouth and vent. 
J. Barrois has observed the development of a considerable number of 
genera [see infra]^ and deduces from these observations a general account 
of the development of the Bryozoa. According to him, the typical form 
of the larva is that of a gastrula, which exhibits two opposed faces 
separated by a circle of cilia (couronne) ; one of these faces is oval, 
having in its centre the mouth, and can be contracted into a kind of 
entry (vestibule), overlapped by the extension of the other or ab-oral 
face, which generally has a greater volume. All larvm exhibit a middle 
layer (feuillet moyen), which is muscular or fatty, and is divided into 
an oral and an ab-oral part ; the latter is more constant and voluminous, 
and constitutes the essential portion of the mesoderm ; it is formed in 
most cases by a simple delamination of the ectoderm, but in the Endo- 
procta the intestine also appears to take part in its formation. The 
larvae of the Endoprocta are differentiated from this common type by the 
development of three special organs for taction, which are originally por- 
tions of the mesoderm, but come into close relationship with the outside; 
the larvae of the Cyclostomata by the development of the crown of cilia 
into a mantle-like expansion ; the larvae of the Chilostomata and Cteno- 
