Family 8. — BRACHIONJEA. Charader. Loricated Rotifers, with a double rotatory organ.
The external covering of these animals is a testula, such as is possessed by the tortoises, not a scutellum, as found in the Crustacea. The motory system consists partly of external organs, and partly of internal muscles. The rotatory apparatus is often apparently com posed of five parts—three in the middle and one on each side. The latter only can be regarded as the true rotatory organs ; the middle portions are only ciliated frontal pro cesses. In the genus Synchceta there are two sette in the rotatory organs, which are also possessed by the Brachiontea. Noteus and Brachionus have a furcate foot, Anurcea is foot less, and Pterodina has a kind of sucker in its place. The nutritive organs are very similar to those of the Hydatinma and Euchlanidota. Intestinal glands have been observed in all the species. The reproductive organs consist of an ovarium, with a few large eggs, which are not hatched internally, but, with the ex ception of Pterodina, are externally attached to the parent after expulsion. The male organs consist of glands and contractile vesi cles. The vascular system is composed of tremulous gill-like organs, and a respiratory spur or tube in some species. Noteus has no eyes, but a large cerebral ganglion ; the other genera have eyes.
With the exception of Notens, the genera of this family were known to the older ob servers. Three species of Anurzea were de scribed by Miiller in 1776, and Joblot disco vered the Brachionus pail (fig. 296.) in 1716.
large quantities that they render the water turbid in which they exist.
Doyere has constructed a family which he calls Tardigrades,and which are most properly included in the class of Rotifera. The ani mals of this family have an elongated body, contractile like that of the Rotifer, with four pairs of short legs, each bearing two pairs of small claws. The alimentary canal is narrow, prolonged into a siphon at its anterior ex tremity, with an internal maxillary apparatus, moveable, and consisting of a muscular bulb traversed by a straight canal, furnished with horny articulated pieces. Until this family
was investigated by Doyere, it was supposed to consist of but one species, the Water-bear (Wasser-Mr) of Eichorn ; but under the name The Pterodina patina was described by Eichorn in 1775. The genus Brachionits is, of all the Rotifers, the most remarkable for the density of its lorica. The thickness of this organ pre vents their internal structure from being so plainly obset ved as that of many other genera. The species of Brachionus often occur in so of Ilfacrobiotus, Arctiscon, and other names, which were supposed to be synonymous, it appears that several animals were confounded, for which Doyere proposes the generic terms Emydia, Milnesia, and Macrobiotus. These animals are found in the same localities as the common Rotifer, and like it possess the same faculty of resuscitation after desiccation. On account of the slow movement of Macro biota:, they have been called Tardigrada ; an objectionable term, because applied to a family higher up in the scale of development. On account of their habit of crawling, and not swimming as the great mass of Rotifers, Du jardin names them Systotides marcheurs. They are interesting as connecting the Rotifers, not only with the Annelida. but also, through their foar pair of feet, with the higher forms of' the Articulata, and on the other side with the Helminthida. Ehrenberg regards Macro biotus not as a Rotifer, but as an animal re lated to Lerncea. This epizoon and its con geners have undoubtedly more affinity with the articulate than with the molluscous tribes ; and the relation of the Tardigrades with the Rotifers eqablishes for that family a more decided tendency towards the articulate groups than any other.
Although the organisation of the Rotifera is included in too small a space to permit of dissection, the transparency of their integu ments is so great as to permit of an easy ex amination of their internal organs. From the previous descriptions of the families of this order, it will be seen that their organis ation is very complicated, and that their size is by no means the measure of their position in the animal scale.