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/lit29465/58/
48 POLYPIFERA. 
We do not doubt that all polyparies, whether 
flexible or calcareous, are formed in a similar 
manner, the horny matter of one and the 
calcareous axis of the other being entirely 
produced by the conversion of soft gelatinous 
matter into hard substance through the agency 
of the membrane which always invests the 
polypes. Moreover, this infundibular mem¬ 
brane must offer a thousand modifications of 
form in different families, genera, and even 
species. Sometimes it is very extensive and 
irritable ; at others, adhering to the parietes 
of the cells throughout their entire length ; the 
polype is immovably fixed at the opening of 
its tube. We consider this membrane as one 
of the most essential organs for the produc¬ 
tion of the polypary, having observed it in 
Flustræ, Sertulariæ ; and, as far as we know, 
the same is the case in Madreporigenous 
polypes. 
When the calcareous tube has grown to a 
certain height, the animal proceeds to form 
the external horizontal stage, by means of 
which it becomes united to the tubes in its 
vicinity. In order to effect this the soft in¬ 
fundibular membrane spreads itself out hori¬ 
zontally, so as to form by its duplicature a 
kind of rim round the margin of the tube 
(fig. 2, a) ; in this state it loses the irritabi¬ 
lity that it previously possessed, and its two 
opposed surfaces becoming united to each 
other, it is gradually solidified by the depo¬ 
sition of calcareous matter in its substance, 
so as to form a firm horizontal plate. It 
generally happens that several of the neigh¬ 
bouring polypes construct similar horizontal 
stages at the same time, and precisely upon 
the same plane, in which case all the stages 
coalesce at their circumference, and become so 
intimately conjoined as to form but a single 
floor, which, when calcified, exhibits no marks 
whatever of the union which has been thus 
effected. After the formation of this stage 
the growth of the tube again proceeds up¬ 
wards, in the same manner as before, until it 
arrives at its full height. 
It is difficult to say how the ova formed 
upon the ovigerous filaments make their 
escape ; for, seeing their size, it seems impos¬ 
sible for them to pass out by the mouth ; and 
it seems more probable that it is not until a 
polype dies that the germs of its progeny leave 
the tube of their parent, and settling down 
upon the horizontal stage constructed by the 
preceding generation commence their deve¬ 
lopment. 
When first attached in this position the 
young Tubipore exhibits not the slightest 
trace of the future polype, but consists of a 
simple gelatinous membrane folded upon itself 
so as to resemble a little turban. This 
turban-shaped mass gradually elongates itself 
by its upper part, and, as its development 
proceeds, produces a polype in its interior, 
the tube which encloses it remaining soft and 
flexible above, while it is gradually calcified 
below. And it may here be remarked, that 
from the small diameter of the commencement 
of its tube, it is evident that the animal in* 
creases in all its dimensions during its advance 
to maturity. 
Sertularidœ.— The depths of the ocean are 
inhabited by innumerable zoophytes equally 
remarkable for the beauty of their appearance 
and the peculiarity of their structure ; these 
are the Sertulariæ, whose arborescent stems 
have so much the appearance of vegetable 
productions that they are still regarded by 
the uninformed as “ sea-weeds.” On putting 
a living specimen of a Sertularia (fig. 54) 
Fig. 54. 
Branch of Sertularia geniculata, magnified, showing 
cells, polypes, and ovigerous vesicles. 
into a jar of its native element, and watching 
it attentively with the aid of a magnifying 
glass, its real nature becomes at once appa¬ 
rent, and instead of being of vegetable origin, 
all the elegant ramifications of which it consists 
are found to be peopled with numbers of 
hydriform polypes, all actively employed in 
catching prey, and apparently ministering to 
the support of the general community formed 
by their aggregation. 
The stem of a Sertularia consists of a hol¬ 
low tube, composed of a flexible horny sub¬ 
stance, diversely ramified in different species, 
in the interior of which is enclosed a soft 
animal substance, which constitutes the living 
portion of the zoophyte. At regular intervals 
every branch is studded with little cells, com¬ 
posed of the same horny material as the 
general stem, in each of which is lodged a 
Hydra, or at least a polype similar to the Hydra 
in its general characters, the base of which 
is continuous with the central living pith that
        

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