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61
ikke meget brede, men tiltage i Bredde, saa at de ere
bredest henimod Midten af Kroppen, hvorfra de aftage i
Tykkelse, indtil de mod den bagerste Ende blive yderst
fine. Enhver Radialnerve lober imellem hvert Par
Længdemuskler. under Radialkarret, kun adskilt fra dette og
Huden ved et tyndt Lag Bindevæv, Tab. VIII, Fig. 12.
Fra Radialnerverae udgaa en Mængde Grene til
Huden. Disse ere ved deres Udspring temmelig tykke, men
forgrene sig meget snart og danne dels ganglionære
Opsvulmninger, Fig. 13, c, dels fine, udbredte anastomoserende
Net i Corium, Fig. 13, b, hvorfra udsendes Smaagrene dels
til Musklerne, dels til det ydre Epithellag, hvor de
forsvinde.
Radialnerverne have den samme histologiske Bygning
som Nerveringen. De have en Skede, indenfor hvilken
findes et lysere Cellelag, der ligesom dækker det indre Lag,
som synes at være stribet, Fig. 12, a. Uagtet al anvendt
Møie har det ikke været os muligt at kunne konstatere for
Trochostomas Vedkommende Sempers Iagttagelser med
Hensyn til den finere histologiske Bygning af Radialnerverne
hos Molpadiderne. Han angiver, at Radialnerven hos disse
Dyr er sammensat af 3 flade Baand, tydelig adskilte ved
et tyndt Bindevævsseptum og indesluttet i en Skede. Hos
Trochostoma findes kun to Lag, og disse ere ingenlunde
adskilte ved Bindevæv, men gaa umiddelbart over i hinanden.
Kjønsorganerne.
Slægten Trochostoma har adskilt Kjøn, og afviger
saaledes fra de øvrige Molpadider, som ere antagne for at
være Hermaphroditer. I Dyrets Ydre er der Intet, som
angiver Kjønnet, men i den indre Bygning adskiller Hannen
sig tydeligt fra Hunnen, idet nemlig Kjønsorganerne ere
saa forskjellige i deres Form, at man strax kan afgjøre,
hvilket Kjøn man har med at gjøre.
Kjønsorganerne ere fæstede til den fortykkede Del af
det dorsale Mesenterium, lige ved Tarmens Begyndelse, og
danner to store Stammer, som forene sig til en fælles
Ud-førselsgang, Tab. IX, Fig. 39, 40. Den ene Stamme er
altid noget længere end den anden.
Hos Hunnen udgaar fra den længste Stamme, der
indtager omtrent Kroppens halve Længde, 28—30 dels
rør-formige, dels kolbeformige Udvidninger, der have en
forskjellig Længde og dele sig dichotomisk, og fra den korte
Stamme udgaa 15 — 18 lignende Forlængelser, Fig. 40, a.
Hos Hannen bestaar den længste Stamme af en utallig ’
Mængde lignende Rør, som hos Hunnen, — kun ere de
meget hengere og tyndere, og indtage, idet de ligeledes
dichotomisk dele sig, hele Dyrets Længde. Den kortere
to the integument of the oral disk, and to the tentacles:
also 5 large branches, which constitute the radial nerves.
The latter are not very thick at their origin, but increase
in diameter, being thickest near the middle of the body,
from whence they begin to diminish, till, towards the
posterior extremity, they terminate remarkably slender.
Each radial nerve extends between each pair of
longitudinal muscles, under the radial vessel, separated from the
latter and from the integument by a thin layer of
connective tissue, Pl. VIII, fig. 12.
Numerous branches proceed from the radial nerves
to the integument. At their origin these branches are
comparatively thick, but soon divide, forming ganglionic
protuberances, fig. 13, c, and fine-meshed, anastomosing
network in the corium, fig. 13, b, from which subsidiary
branchlets are sent off, some to the muscles, others to the
outer epithelial layer, where they disappear.
The radial nerves exhibit the same histological
structure as the nervous ring. They are furnished with a sheath,
beneath which extends a lighter-coloured cellular layer,
covering up, as it were, the inner layer, which would seem to
have a striate structure, fig. 12, a. As regards Trochostoma
we cannot, we regret to say, though no trouble has been
spared to arrive at conclusive results, confirm Semper’s
observations, according to which the radial nerves in the
Molpadida; are distinguished by greater complexity in their
histological structure. According to that zoologist, the radial
nerve in these animals is composed of 3 flat bands, distinctly
separated by a thin septum of connective tissue, and
invag-inated in a sheath. In Trochostoma there are bat two
layers, not separated by a connective membrane, but
contiguous, passing one into the other.
O-enerative Organs.
The genus Trochostoma has the sexes separate, and
differs therefore from all other Mölpadidæ, which are
regarded as bisexual. In the habitus of the animal there is
nothing to indicate the sex; but with regard to its inner
organisation, males may be readily distinguished from
females by the obvious difference in form characterising the
generative organs.
These organs are attached to the inspissated portion
of the dorsal mesentery, in immediate proximity to the
origin of the intestine, and constitute two large stems, which
unite to form a common eferent duct, Pl. IX. fig. 39,
40. One of the stems is invariably longer than the other.
In the female, from 28 to 30 expansions, some
tubular, some clavate, varying in length and dividing
diclio-toraously, proceed from the longer of the stems, which
extends about half the length of the body: and from the
short stem proceed 15 -18 similar prolations. fig. 40, a.
In the male, the longer stem consists of a countless
number of tubes similar to those in the female; they
are, however, much longer and slenderer, and extend, too,
dividing dichotomously. throughout the whole length of the
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