When we examine a young branch that is sufficiently transparent, a fluid containing irregular globules is seen to circulate in its interior. There is no intestinal canal, all ex crementitious matters being evacuated through the oral orifice.
Circulation.—The stems of the Tubularidec 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 Eudendriunz, 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 towar& 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 inicroscope ; 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 Tubularid are pro vided with an external tubular sheath, or polypary, which is thin and semitransparent ; its texture is corneous or perganientaceous, 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 this arrangement of the reproductive system may appear, we learn from the researches of Professor Van Beneden that the propagation of the Tubularido is effected by no fewer than five different modes ; namely, 1. By continuous gemmation.
2. By the production of free gemnix.
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 nzode of propagation, by continuous genunation. —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 gemum.
This method of propaaation is the simplest possible, and is effectecIbby mere growth from the oriainal polype in certain determinate points cif 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 gemniza 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 Hydrve, 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 ahnost be induced to regard the different cells composing their bodies as analogous to ova, and the polype itself as a mere aggregation of germs. It 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.