two strap-shaped sexual glands and tile vesicles. Traces of a vasculdr system are seen only in a few species. The sensa In this as in the preceding family, there can be little doubt that the artificial character, the number and position of the so-called eyes, on which the genera are founded, separates species which are united by much more im portant characters. Thus Dujardin remarks, that the genera Lepadella, Metopidia, Ste phanops, and Squaniella are separated only by characters which vary according to the nutrition of the animal and the time of the year. The same remark will apply to many of the genera of the preceding family Hyda tinma. The species of this family are found in both salt and fresh waters, and have a wide distribution over the surface of the earth. The genus Lepadella is developed sometimes in stagnant water in such quan tities as to give it a milky appearance.
Family 7. — PHILODIN/EA. Character.
Naked Rotifers with tvvo rotatory organs.
The body of these animals is mostly of a ten uiform, cylindrical, or spindle-shape, with false articulations, by which, through its muscles, the animal is enabled to withdraw the parts of its body one within another, like the tube of a telescope. The double rotatory organ, so evident in Rotifers (fig. 301.), is seen in all the species. In every species there is a fur cated foot. In the genera Callidina, Rotifer, Actinurus, and Phitodina, appendicular hooks are found on the false articulations (fig. 295.). A muscular system is seen in Callidina, Acti nurus, Rotifer, and Philodina. Three of the genera have two jaws with two teeth, and two jaws with a row of teeth. A filiform in testine, with a vesicular enlargement at the end, is seen in four of the principal genera. Intestinal glands are seen in four genera. The reproductive system is herinaphrodite in four genera, with an ovarium and male sexual glands, and contractile vesicles. The last are only seen in Rotifer and Philodina. These two genera and Actinurus sometimes produce living young. Traces of a vascular system in the transverse vessels of Rotifer and Philodina, and also in the respiratory tube or opening of these genera, and of Actinurus and Mono labis, are seen. Nervous masses are found under the eyes.
This family, which includes the true Ro tifers of Dujardin, embraces some of the least known, as also the most common, animals of the class. The genera Hydrias and Typhlina were found during the travels of Ehrenberg in Asia. Callidina and Monolabis have been found by Ehrenberg at Berlin only. The Rotifer vulgaris was the first wheel-animalcule ever seen, and is certainly the most com mon of the whole class. It was described with great accuracy by Leeuwenhoek in in his early papers on its discovery. It is this animal which has also been most fre quently the subject of the desiccating ex periments to which we have alluded. Acti nurus Neptunius was known to the earlier observers of these creatures as the wheel animalcule with the long foot, on account of the extension of its foot or tail. The Philo dina, though not an unfrequent genus, was first described by Ehrenberg in 1838. The
articulated character of the integument in the ispecies of this family, give them a habit dif ferent from the rest of the group : by means of their probiscoid mouth and prehensile tail, they can successively grasp the object on which they are placed, and are thus enabled to crawl in the same way as the leech and other Annulosa. The affinity between the Rotiferm proper and the Arctiscon and whole family of Tardigrades, which are not ad mitted as Infusoria by Ehrenberg, has been pointed out by Doyere; and there can be little doubt that we have, through this group, a transition from the Rotiferm to the Anne lida.
The Rotifer vulgaris is found very com monly in the ponds and ditches of England, where it attaches itself to the Confervm, the various species of Lemna, and the Cerato phyllum, which are so abundant in these places. M. Morren, of Liege, has recently pointed out a curious habitat for this animal. Rceper, many years ago, observed that this animalcule sometimes penetrated the cells of Sphagnum, and even lived in those parts of the plant which were not immersed in water. Unger described, in 1828, some vesicles in the structure of Vaucheria clavata, which had the power of moving about spontaneously, and which he discovered were produced by an animalcule in their interior. The subsequent researches of Morren showed that this ani malcule was truly the Rotifer vulgaris. It seems to prefer such a situation to its liberty, for Morren says, " One day I opened a protu berance gently ; I waited to see the Rotifer spring out and enjoy the liberty so dear to all creatures, even to imprisoned animals ; but no, he preferred to bury himself in his prison, descending into the tubes of the plant, and to nestle himself in the middle of a mass of green matter, rather than swim about freely in the neighbourhood of his dwelling." The species of Philodina are beautiful ani malcules. P. roseola has a rose colour of its whole body ; and the ova, when deposited, have a reddish colour. The ova of this ani malcule are deposited in little heaps, which the parent attends to, and even remains with the young ones after they are hatched, which Ehrenberg attributes to a kind of social in stinct. Professor Agassiz found this creature amongst the animalcules which contribute to the colour of the red snow. It was at one time supposed that this colour was due to a species of Alga, the Protococcus nivalis. Mr. Shuttleworth, of Berne, was the first to an nounce that he had found, in addition to the cells of a plant, several species of Polygastria, beloneing probably to the genus Astasia. Subsequently to this announcement, Professor Agassiz discovered the presence of this ani malcule in the same situation. The author of this article has found Philodinaroseola in com pany with a red animalcule, apparently a species of Astasia, in waters slightly im pregnated with sulphuretted hydrogen. Ehren berg says this animal sometimes occurs entirely colourless, so that its colour may depend on its food.