POLYPIFERA. 



interior. There is no intestinal canal, all ex- 

 crementitious matters being evacuated through 

 the oral orifice. 



Circulation. The stems of the Tubularidfe 

 are formed of the same kind of tissue as that 

 which constitutes the body of the Polype, and 

 each stem is hollow throughout its entire 

 length. The tube thus formed is filled with 

 a fluid containing globules, which is constantly 

 in motion, a circumstance first observed by 

 Lister *, but its course is by no means regu- 

 lar. Sometimes the globules mount up as far 

 as the body of the polype, and then descend 

 again by the same route; if they come to a 

 division of the stem, as is frequently the case 

 in most genera, they may be sometimes seen 

 first to penetrate into one branch, and then 

 returning enter the other. In the ordinary 

 Tubularia, described by Lister, a current may 

 generally be seen ascending along one side and 

 descending along the other. In the long and 

 slender stems of Eudendrium, which are very 

 transparent, Professor Van Beneden has ob- 

 served the fluid containing globules mount 

 from the base towards the summit for some 

 instants, when the circulation seems to be- 

 come suspended for a time ; but soon the 

 globules begin to move in the opposite di- 

 rection, descending from the summit towards 

 the base ; shortly after it again mounts as at 

 first, and thus the circulation goes on alter- 

 nately up and down. This movement of fluid 

 in the stem Professor Van Beneden is disposed 

 to attribute to ciliary action, although no cilia 

 are discoverable by the microscope ; still, 

 without such mechanism, it is difficult to ac- 

 count for two distinct currents running in 

 opposite directions in the interior of the same 

 tube, which exhibits not the slightest trace of 

 a septum between them. 



There seem to be no organs specially ap- 

 propriated to respiration. 



With the exception of the genera Coryne 

 and Hydractinia all the Tubulariclae are pro- 

 vided with an external tubular sheath, or 

 polypary, which is thin and semitransparent ; 

 its texture is corneous or pergamentaceous, 

 and very flexible. The polypary of the genus 

 Tubularia is generally described as being a 

 simple tube without any ramifications ; this, 

 however, is only true in the case of young 

 individuals inhabiting isolated stems. In old 

 specimens the polypary is ramified at its base, 

 and is only straight and simple at its free 

 extremity. 



Reproduction. In all the genera of this 

 family the reproductive organs consist of groups 

 of little pedicles growing in the vicinity of the 

 tentacula, which support little rounded bodies, 

 often united together in bunches, which when 

 mature fall off like fruit from a tree, and are 

 dispersed to form new colonies. It is a true 

 animal seed, which the waves carry to a dis- 

 tance and disseminate in all directions, and 

 the whole observable reproductive apparatus 

 consists of the organs that produce these 

 rounded corpuscles or ova. Yet simple as 



* riiil. Trans, for 1831, pt. 2. 



this arrangement of the reproductive system 

 may appear, we learn from the researches of 

 Professor Van Beneden that the propagation 

 of the Tul) it la rides is effected by no fewer than 

 five different modes ; namely, 



1. By continuous gemmation. 



2. By the production of free gemmae. 



3. By simple ova. 



4. By ova with a multiple vitellus. 



5. By free gemmation and ova combined. 

 Observation has moreover shown that in 

 every species propagation is effected by more 

 than one of these modes of reproduction, and 

 sometimes by three or four ; and it must be 

 remarked that in none of them is the co- 

 operation of a male apparatus requisite, nei- 

 ther have any male organs or spermatozoa 

 been as yet detected. 



First mode of propagation, by continuous 

 gemmation. This is the ordinary form of 

 gemmiparous generation, whereby a colony is 

 developed by sprouts derived from a single 

 individual ; the appellation " continuous gem- 

 mation," is applied to it by Professor Van 

 Beneden, to distinguish it from the second 

 mode of reproduction by free gemmae. 



This method of propagation is the simplest 

 possible, and is effected by mere growth from 

 the original polype in certain determinate 

 points of its substance, which points are simi- 

 larly situated with respect to each other in 

 all the individuals belonging to the same spe- 

 cies. At these points gemmae appear exactly 

 similar both in texture and mode of growth 

 to the body from which they spring ; and 

 these buds as they grow give birth to others 

 in a precisely similar manner. All these ani- 

 mals, be it remembered, are, like the Hydras, 

 capable of being reproduced by the mecha- 

 nical division of their bodies, so that if one 

 be cut into several fragments, each portion 

 may give rise to a new individual ; every part 

 of their structure is endowed with a repro- 

 ductive power comparable to that which is 

 conferred only upon the eggs of the superior 

 animals ; whence we might almost be induced 

 to regard the different cells composing their 

 bodies as analogous to ova, and the polype 

 itself as a mere aggregation of germs. ]t is 

 upon the definite points whence these buds 

 sprout that the particular characters of the 

 Polyparies depend, else they would mostly 

 resemble each other, for at their first pro- 

 duction there is little difference to be observed 

 between them. 



In like manner when a stem is cut off trans- 

 versely, a bud is developed from the cut ex- 

 tremity, which by its growth prolongs the 

 original trunk. When this kind of gemma 

 has attained to a sufficient size there arises 

 from its extremity a little crown of tubercles, 

 and subsequently a second becomes manifest 

 at some distance from the first ; and as the 

 growth of these tubercles continues, each of 

 them becomes at length developed into a ten- 

 tacle. The tentacle, therefore, grows from the 

 body exactly in the same way as the bud from 

 the stem, the only difference being that the for- 

 mer is solid, and the latter tubular. 



