Tubiporidce.— The polypary of the Tubi three rows of fleshy papillx. Beneath the opening of the mouth is the stomachal saccu lus, around which arise the eight ovigerous filaments. Those filaments near their origin are loose and floating, but lower down they become connected with the soft membrane (fig. 53. 1, 2, d), with which the tube is lined, pora (17g. 52.)consists of several stages of cy lindrical tubes placed parallel to each other, or very slightly diverging. These tubes are sepa rated from each other by considerable intervals, but mutually support each other by the inter position orexternal horizontal plates formed of the same dense substance as themselves, by which they are united together, so that a mass of these tubes exhibits an arrangement some thing like that of the pipes in an organ ; whence the trivial name musica by which the species is distingu:shed. From the upper ends of these tubes the polypes are protruded, and being when alive of a bright grass green colour they contrast very beautifully with the rich crimson of the tubes they inhabit. The mouth* of the polype is suspended in the centre of the tube by means of the soft mem brane : it is surrounded with eight tentacula, the margins of which are fringed vvith two or throughout its whole length, but gradually diminishing in thickness as they descend. These filaments are equivalent to the ovigerous tubes of the other Anthozoa; but the ova are here developed upon their external surface, to which they are attached by short pedicles.
Extending between the roots of the tenta cula of the polype and the margin of the tube is the membrane, which, in the retracted state of the animal, is drawn into the shape of a funnel, the mouth of the funnel being con tinuous with the extremity of the calcareous tube. The funnel-shaped membrane is in fact a continuation of the calcareous tube, from which it only differs in texture from the cir cumstance that the latter has become solidi fied by the interstitial deposition of calcareous matter in its substance, while the former still retains its softness and irritability.
The funnel-shaped membrane does not ter minate suddenly upon the calcareous tube ; the latter, indeed, is a prolongation and pro duct of it ; the calcareous substance is depo sited in this gelatinous membrane in the same manner as phosphate of lime is deposited in the bones of very young subjects, changing its soft texture into hard and solid substance. The manner, therefore, in which this tube is formed cannot be compared to the mode of formation of the cells of Serpulm or the tubes of Mollusca ; in the latter it is a secretion of the skin, almost an epidermic product. In polyparies, on the contrary, there is a real change of soft into solid substance, which is effected gradually, but the calcareous matter is not deposited in layers.
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 Flustrw, Sertularim; 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 np 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.