Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29465/54/
POLYPIFERA. 
44 
longitudinal prominent bands, the free edge 
slightly enlarged and rounded, a pedicle in 
the middle like the stem of the vase, and the 
transparent vesicle lining its interior through¬ 
out. 
Fig. 49. 
A series illustrating the development of Tubularia hy 
free gemmae, from the first indication of the bud to 
the time when it becomes detached. 
1. A hollow tubercle or elevation, in the interior 
of which a movement or circulation of the glo¬ 
bules, indicated by the arrow, takes place; a, a 
cell just beneath the surface. 
2. The same, showing the cell more advanced ; a, 
indicates this cell in all the figures. 
3. This, and the following figures, represent the 
development of the gemma more and more ad¬ 
vanced; b, a tubercle, situated beneath the cell, 
which becomes the stomach of the embryo; this 
organ is indicated by the same letter in the other 
figures. 
4. c, tubercles shooting up from the sides ; they 
are hollow, and communicate with the cavity of the 
stomach, and are the first indication of four vessels 
proceeding from the stomachal cavity. In the fol¬ 
lowing figures the letter c indicates these vessels. 
5. b, the tubercle become more elevated, indenting 
the cell a ; the four secondary tubercles, c, more 
distinct and prominent. 
6. The stomachal and its four surrounding hollow 
tubercles still further prolonged. 
7. In this figure the four smaller tubercles have 
become vessels, and united with one another in front. 
8. The four vessels have more completely united 
in front ; the arrows here, as in the other figures, in¬ 
dicate the current of the circulating fluid. 
9. d, The first indications of the tentacles," con¬ 
sisting of tubercles sprouting from the four vessels. 
10. The tubercles, d, at the end of the four ves¬ 
sels, c, have become sufficiently elevated to make 
a projection on the exterior. 
11. These tubercles, become considerably salient 
externally, are now manifestly the four tentacles of 
the embryo. 
12. Minute cells are now visible at the extremity 
of the tentacles. 
13. The tentacles still more advanced ; the line 
of separation of the embryo from its stalk become 
distinctly visible. 
14. Hitherto the stomachal cul-de-sac has pro¬ 
gressively increased,- it now begins to diminish, and 
the cell a, or the space between it and the external 
envelope becomes opened at e, forming a kind of 
mouth ; the embryo is now capable of great exten¬ 
sion; the pedicle is constricted at the point of 
insertion and its internal cavity nearly obliterated. 
(From Van Beneden.') 
The different phases of the development 
above described will, however, be best under¬ 
stood by a reference to the series of figures 
which we have appended, carefully copied 
from Professor Van Beneden’s elaborate illus¬ 
trations. 
The joung Tubularia has now assumed the 
appearance of a Beroe, and in this condition 
has doubtless been often mistaken for an in¬ 
dividual belonging to the class Acalephæ ; and 
lively contractions of its body are frequently 
witnessed, although it still remains attached 
to its pedicle. 
At the extremity of each of the four longi¬ 
tudinal vessels a little tubercle now becomes 
developed, which, as it becomes elongated, is 
converted into a tentacle, or sometimes, as in 
Eudendrium, by its bifurcation, two tentacula 
are formed from each tubercle. 
At this period of its development the young 
Tubularia spontaneously detaches itself from 
the parent stem, presenting at the moment of 
its separation the appearance of a balloon, or 
rather of a melon. (Fig. 50.1,2,3.) Its contrac¬ 
tions become more and more lively, and it is 
by the aid of these movements that its sepa¬ 
ration is effected. The two poles of its 
globular body may be seen to approach each 
other, and to separate alternately, with a 
movement of systole and diastole similar to 
what is observable in many Medusae. No 
traces of cilia are observable either externally 
or in the interior of its body. In this con¬ 
dition it presents an externai covering, which 
is, so to speak, merely a derivation from the 
integument of the parent polype : this cover¬ 
ing presents somewhat more consistence than 
the internal parts, and is open in front. 
A second membrane lines the preceding 
throughout its whole extent ; like the former, 
it is quite transparent, and at the anterior 
opening (
    

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