Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/184/
172 
ANNELIDA. 
--------A 
is contained in the rest of the apparatus. 
These organs (fig. 74, g) are generally regarded 
as accessory vesicles, and they vary both in 
number and form in different species. 
The female apparatus is of much less mag¬ 
nitude, but also presents a sufficiently com¬ 
plicated structure : it is situated between the 
two canals leading to the accessory vesicles of 
the male apparatus, and is a little posterior to 
the penis. The external orifice, of which we 
have already spoken, communicates with a short 
canal (fig. 74 and 76, A), of a greyish colour, 
which leads to a sort of 
pouch (i). This, accord¬ 
ing to some authors, 
is analogous to an ute¬ 
rus, but in the opi¬ 
nion of other natura¬ 
lists is merely a copu¬ 
lative vesicle for the pur¬ 
pose of retaining the 
fecundating liquid which 
is there deposited by 
the male in the act of 
copulation. This sac is bent upon itself, and 
a duct (J) may be observed to be continued 
from the anterior extremity which leads to the 
ovaries (k) : these are small whitish bodies two 
in number, and in close approximation to one 
another. 
In the earthworm, the only parts that can be 
regarded as male organs are some sacs or 
vesicles vaiying in number from two to seven, 
and situated in a longitudinal series on either 
side of the ventral aspect of the body towards 
its anterior extremity. Each of these vesicles 
adheres to the parietes of the splanchnic cavity, 
by a small canal opening directly outwards by 
pores placed on the posterior and inferior part 
of the corresponding ring: there is farther a 
canal of communication, which is continued 
directly from one vesicle to another of the 
same lateral series ; and at the season of co¬ 
pulation there is found in the interior of these 
organs a viscid liquid abounding with seminal 
microscopic animalcules. The outlets of the 
female apparatus occupy the sixteenth segment 
of the body, and are continuous internally 
with two narrow canals directed forwards, and 
situated on the internal side of the above 
mentioned vesicles. Having reached the ova¬ 
ries, each of these canals (fig. 77, a) divides 
into two branches (A), 
which bend inwards and 
terminate by a globular 
enlargement (c). This is 
seen with the assistance of 
the microscope to be itself 
formed by a continuation 
of the canal puckered up 
into numerous folds,which 
are enveloped in a com¬ 
mon membrane. To each 
of these enlargements are 
appended a pair of ova¬ 
ries, the entire number 
of which is consequently eight, four on either 
side. The colour of these ovaries is whitish, 
their texture pulpy, and their interior is beset 
Fig. 77. 
with numerous minute vesicles, which are the 
ova. At the period of copulation the ovaries 
are filled with a whitish fluid, which is pro¬ 
bably the spermatic secretion, but it is not 
easy to comprehend how the male apparatus 
can introduce it into that part.* According 
to Redi, the ova, after being detached from the 
oviduct, pass along the whole extent of the 
body towards the vicinity of the anus, whence 
they are expelled by two orifices stated to be 
near the termination of the alimentary canal 
or to open in its interior. According to Mon- 
tegre it is the foetus and not the ovum which 
traverses the body to escape by the above 
passages, and the lumbrici according to this 
view are viviparous. This statement has been 
adopted by many authors without perhaps 
sufficient examination ; but, according to recent 
observations by Dugès, it would seem not to 
be correct, and that what have been regarded 
as the young of the earthworm are in fact a 
species of intestinal worm. 
In the nais the male organs are less nume¬ 
rous than in the lumbrici, but differ very little 
in other respects. They consist of a single 
pair of vesicles opening externally by a wind¬ 
ing canal, which terminates by a small fissure 
on the eleventh segment of the body. The 
ovaries are disposed in four principal masses, 
between which there winds a long oviduct, 
of which the extremity can be protruded out¬ 
wardly like a penis.-j- 
In some annelida, as the clepsina carena, 
the ova are developed and hatched before 
exclusion, so that the young are born alive; 
but most of the class are oviparous, and what 
is very remarkable, the same ovum sometimes 
incloses the germs of many embryos : this is 
the case in the earthworm, each ovum of which 
produces two individuals, and in the leech the 
ova contain severally as many as eighteen 
embryos. One might at first view suppose 
that the same circumstances obtained in the 
nais ; but what appears to be an ovum with 
multiplied germs is in reality nothing more 
than an aggregate of simple ova. 
Reproduction.—Some annelida not only per¬ 
petuate the race by the ordinary modes of gene¬ 
ration, but enjoy the singular faculty of pro¬ 
ducing new individuals by a transverse division 
of the body. A nais or an earthworm cut in 
two and placed under favourable circum¬ 
stances, will continue to live, and each moiety 
will become, in appearance at least, a perfect 
animal. This fact, which was first determined 
by Reaumur and Bonnet, has since been veri¬ 
fied by M. Dugès, Sangiovanni, and many 
other observers : the anterior portion of the 
animal reproduces a new tail, and the posterior 
portion developes a head. 
That faculty which the two portions of the 
earthworm’s body possess of manifesting the 
vital properties independently of one ano¬ 
ther, and even after having been separated, 
may be explained to a certain degree by 
the known structure of these animals and 
* See Willis, Dugès, &c. 
f See Dugès, op. cit.
        

Nutzerhinweis

Sehr geehrte Benutzer,

aufgrund der aktuellen Entwicklungen in der Webtechnologie, die im Goobi viewer verwendet wird, unterstützt die Software den von Ihnen verwendeten Browser nicht mehr.

Bitte benutzen Sie einen der folgenden Browser, um diese Seite korrekt darstellen zu können.

Vielen Dank für Ihr Verständnis.