POLYPIFEKA. 



11 



tion with each other, or forms in other words 

 the body of the community, and from this 

 common body buds are thrown out, from 

 which ramifications are produced in all re- 

 spects resembling those met with in the 

 vegetable kingdom ; these constitute the trunk 

 and branches of a tree, which, instead of 

 bearing flowers, produces polypes provided 

 with tentacula, a digestive cavity, and most 

 frequently a reproductive apparatus. 



Tentacular apparatus. In the Tubularidae 

 the tentacula are situated, as in all polypes, 

 around or in the immediate vicinity of the 

 oral opening. Their number is very various, 

 even in the same species, but the variations in 

 their length are more apparent than real, for 

 their contractile powers are such that they 

 are constantly changing in their shape and 

 dimensions, in which respect they resemble 

 the Hydra described above. It is towards 

 the extremity of the tentacle that this con- 

 tractile power is most remarkable ; and when 

 the organ is not fully stretched out, it is 

 enlarged or dilated near the end, insomuch 

 that some authors have erroneously looked 

 upon this part as performing the office of a 

 sucker. 



The disposition of the tentacula varies in 

 different genera. The genus Eudendrium has 

 a single row of tentacula, which are alternately 

 placed a little more internally and externally. 

 The genus Tubularia, properly so called, has 

 a second row of shorter tentacles immediately 

 surrounding the proboscidiform prolongation 

 which constitutes its mouth, and in the genus 

 Stipula (Sars) there is an additional row 

 situated between these two, so that there are 

 genera with one, two, or several rows of ten- 

 tacula ; the lower row is, however, always 

 the longest, and it is these that are persistent 

 when there is only one rank. The tentncula 

 are arranged in whorls in all the Tubularidae, 

 except in the genus Syncori/na, in which they 

 are distributed without regularity (fig. 4-7). 

 No cilia are perceptible, either externally or 

 in the interior of these tentacula, which, 

 when highly magnified, appear to be entirely 

 composed of transparent cells, closely agglo- 

 merated, and no traces of muscular fibre are 

 by any means to be detected ; their move- 

 ments seem to depend entirely upon the con- 

 tractions of their component cellules, which 

 are seen to diminish in size when the tentacle 

 is shortened, and to expand during its elon- 

 gation, preserving nearly the same shape, 

 whence it may be concluded that their pari- 

 etes are endowed with contractile powers. 

 Professor Van Beneden indeed compares them 

 to so many hearts placed end to end, which, by 

 their dilatation elongate, or by their con- 

 striction shorten or bend, the tentacle of 

 which they constitute the substance. 



Digestive system. In the Tubularidae there 

 is seen, situated in the middle of the ten- 

 tacula, a sort of proboscidiform appendage, 

 open in the centre, which is the entrance 

 to the digestive cavity. The name of pro- 

 boscis appears sufficiently applicable to this 

 part, both on account of its situation and of 



the changes of form which it continually un- 

 dergoes. In its most usual condition it has 

 the appearance of a protuberance provided 

 at its summit with an orifice of very variable 

 shape and size.* 



Fis. 47. 



Syncoryna pusllla. 



1. A little group, twice the natural size. 2. A 

 branch much magnified, a, the stalk ; b, a bud from 

 which a polype is about to be developed ; 6, a bud 

 which is about to give rise to a long stalk ; c, body 

 of the Syncoryna with its three rows of tentacula ; 

 d, a Syncoryna having only two rows of teutacula. 

 (After Van Beneden.) 



The cavity of the proboscis leads into that 

 of the stomach, but neither the one nor the 

 other have parietes proper to themselves, but 

 on the contrary seem, as in the Hydra, to be 

 mere excavations in the substance of the 

 polype. In the genus Coryne, the cavity of 

 the stomach is circumscribed, so that each 

 polype has a proper digestive cavity ; but in 

 all the other genera belonging to this family, 

 the stomachal receptacles of different indi- 

 viduals communicate mediately one with 

 another, so that what is taken into the sto- 

 mach of one polype may pass into those of 

 all the individuals composing the colony. 

 Thus, what is eaten by a few individuals pro- 

 fits the whole community, seeing that what 

 one swallows may pass into the stomachs of 

 its neighbours. 



When we examine a young branch that is 

 sufficiently transparent, a fluid containing 

 irregular globules is seen to circulate in its 



* Recherches sur 1'Embvyogenie des Tubulaires, 

 et FHistoire naturelle des clifferents Genres de cette 

 Famille qui habitent la cote d'Ostende, par P. J. 

 Van Beneden, Mem. de 1'Acad. IJovale de Bruxelles, 

 1844. 



