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 

 Flustrac, Sertularia?; 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 

 (jig. 2, ) ; 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. 



SertularidcE. 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 Sertulariae, whose arborescent stems 

 have so much the appearance of vegetable 

 productions that they are still regarded by 

 the uninformed as " sea-weeds." On nutting 

 a living specimen of a Sertularia (jig- 54) 



Fig. 54. 



Branch of Sertularia geniculata, magnified, showing 

 cells, polypes, and ocigerous 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 



