of teeth for chewing (fig. 289. a, a), two creatic glands. Ova and ovaria have been Fig. 289.
These genera embrace six species, some of which have been known to microscopic ob servers under various names, from a very early period. Icthydium podura was described by Joblot, as poisson a la tete treflee, in 1718. The Chcctonotus larus was described by Miller in 1776 as Trichoda acarus.
This family embraces some of the simplest forms of the Rotifera. It may perhaps be doubted as to whether this class at all is the place for the genus Chalonotus. They have no distinct rotatory organ, and their bodies covered with cilia, place them in very close alliance with some forms of the Polygastria, especially the Euplota, from which they are distinguished by their symmetry,and distinctly furcated tail. Dujardin places Chectonotus amongst his symmetrical Infusoria, which do not include the Rotifera or Systolides.
Family 2.—CEcisTuslit. Character. Ro tiferous animals, with a single rotatory organ entire at the margin, enclosed in a shield.
The organs of motion consist of internal muscles and an entire foot or tail. The or gans or nutrition are an annaratus with rows observed in the two forms of which the family consists. Vessels, two filiform tremulous gans (called by Ehrenberg "gills"); nervous fibres, with ganglia, are seen in Conochilus, and two red eyes are seen in both genera.
I Confined to an in Lorica, or (Ecistes.
4 dividual.
shield.
(Ammon to many. Conochilus.
In the less circular rotatory organ than in Plygura we see the tendency in these animals to the more compound forms of that organ. The lorica, in this family, is not homologous with this organ in many of the other loricated species ; but a case formed by a secretion from the surface of the body of the animal, as is seen in some Annelides, and occasionally in the aquatic larvae of insects. The social habit of Conochilus is very remarkable in this group, as many as forty individuals being frequently found together, attached by their tails, and the consequence of the action of their rotatory organs is a circular movement of the whole mass (fig. 290.). This habit is not confined to Conochilus amongst the Roti fera ; but it is interesting as connecting this class in habit with the compound Polygastria on the one side, and the Cirripedia and com pound Ascidia on the other.
to answer to the description of the family. Cyphonautes is a marine animal, of which Eh renberg has seen but two specimens. Micro codon has also doubtful characters. Megalo trocha, of which there is only one species, M. albo:fiavicans, has often been described by the older observers.
Family 3.—MEGALOTROCHCEA. Character.
Monotrochous rotatory animals, with the mar gin of the rotatory organ incised or flexuous, not inclosed in a shield.
The flexuous extended rotatory organ is used for locomotion, swimming, and the sup ply of nutriment. Muscular bands are evident m the interior, by which the form of the body is changed. In Megalotrocha, the alimen tary canal is supplied with a stomach, two cmca, jaws with a double row of teeth, and two pancreatic glands. In the other two species there is a single canal, without sto mach or cmca. Microcodon has jaws with two teeth. Cyphonautes is toothless. The re productive organs consist of an ovarium. The ova in Megalotrocha are attached to the parent by a thread. Vessels, and tre mulous gill-like organs, are observed in Megalotrocha. The organs of the senses are in two genera the red eyes. Mega lotrocha exhibits radiated nervous masses, and above these four dark glandular bodies in the neighbourhood of the mouth. These have been erroneously regarded as eyes ( fig. 291.).
Family 4. — FLOSCULARIA. Character.
Monotrochous loricated Rotifers, with a ro tatory organ, with sinuous lobed or multifid margins.
The rotatory organ is divided more or less deeply into two, four, five, or six divisions. In the last case they may be almost said to be compound. The alimentary canal gene rally exhibits a stomach, and is supplied with jaws and teeth. Floscul Iria has no stomach. Lacinularia has two cmca. Semilunate pan creatic glands are seen in all the species. A short ovarium, producing a few ova at a time, is found near the foot in all the genera. Male organs, as glands, exist in Lacinularia and Melicerta, perhaps also in Floscularia and Stephanoceros. Vessels are seen in Lacinu laria. Tremulous gill-like organs in Stephano ceros and Lacinularia. Eyes are seen in all except Tubicolaqa. Nerve-like ganglia may be found in Lacinularia, Limnias, and Meli certa. Two pairs of muscles contract the body posteriorly (fig 5.).