Page:EB1911 - Volume 14.djvu/593

 unknown. The endosarc is full of food-granules and reserve-granules (oil, colouring matter and proteid).

The meganucleus and the micronucleus are both usually single, but in Dendrosoma (fig. viii. 20), of which the body is branched, and the meganucleus with it, there are numerous micronuclei. In most cases the micronucleus has not been recorded, though from the similarity of conjugation, and its presence in most cases of fission and budding that have been accurately described, we may infer that it is always present. In unequal fission the meganucleus sends a process into the bud, while the micronucleus divides as in Ciliata. The bud may be nearly equal to the remains of the original animal, or much smaller, and in that case a depression surrounds it which may deepen so as to form a brood-cavity, either communicating by a mere “birth-pore” with the outside or entirely closed. In some cases the budding is multiple (fig. viii. 8), and a large number of buds are formed and liberated at the same time. In all cases the bud escapes without tentacles, and possesses a characteristic supply of cilia, whose arrangement is constant for the species.

In some cases an adult may withdraw its tentacles, moult its pellicle and develop an equipment of cilia and swim away: this is the case with Dendrocometes, parasitic on Gammarus, when its host moults.

The numerous species of Suctoria, often so abundant on various species of Cyclops, are not found on the other freshwater Copepoda, Diaptomus and Canthocamptus, belonging indeed to other families. Again, these Suctoria affect different positions, those found on the antennae not being present on the mouth parts; the ventral part of the thorax has another set; and the inside of the pleural fold another. Rhyncheta occupies the front of the “couplers” or median downgrowths uniting the coxopodites of the swimming legs, and Choanophrya settles in the immediate neighbourhood of the mouth, preferably on the epistoma, labrum and metastomatic region, but also on the adoral appendages and in rare cases extends, when the settlement is extensive, to the bases of the two pairs of antennae; while distinct species of Podophrya settle on the antennae, the front of the thorax and the inside of the pleural folds. Dendrocometes is common on the gills of the freshwater shrimp (Amphipod) Gammarus and Stylocometes on the gills and gill-covers of the Isopod Asellus, the water-slater. The independence of the Acinetaria was threatened by the erroneous view of Stein that they were phases in the life-history of Vorticellidae. Small parasitic forms (Sphaerophrya) were also regarded erroneously as the “acinetiform young” of Ciliata. They now must be regarded as an extreme modification of the Protozoon series, in which the differentiation of organs in a unicellular animal reaches its highest point.

1. Unstalked simple forms. Urnula Cl. and L., permanently ciliate; Rhyncheta Zenker (fig. viii. 1), on the limb couplers of Cyclops; Sphaerophrya Cl. and L. (fig. viii. 2-6, 12), endoparasitic in Ciliata and formerly taken for embryos thereof, never attached; Trichophrya Cl. and L. (fig. viii. 7), of similar habits, but temporarily attached, sessile.

2. Stalked simple forms; Podophrya Ehr. (fig. viii. 10, 13, 16), tentacles all knobbed or flared; Ephelota Strethill Wright, tentacles all pointed; Hemiophrya S. Kent (fig. viii. 8, 9, 14), tentacles of both kinds; Choanophrya Hartog, tentacles thick, truncate, very retractile, when expanded opening into funnels for aspiration of floating prey, never for attachment—epizoic on antero-ventral parts of Cyclops.

3. Cupped forms; Solenophrya Cl. and L., cup sessile; Acineta Ehr., cup stalked; Acinetopsis Bütschli, like Acineta, but the cup flattened, closed distally with only slit-like apertures (“pylomes”) for the bundles of tentacles; Podocyathus, like Acineta, but with pointed as well as knobbed tentacles.

4. Tentacles in bundles at the tips of one or more processes or branches of the body. Ophryodendron Cl. and L., tentaculiferous process single (fig. viii. 21); Dendrocometes Stein (fig. viii. 15), body rounded, processes repeatedly branched, epizoic on gills of Gammarus pulex; Dendrosoma Ehr. (fig. viii. 17-20), body freely branched from a basal attached stolon, meganucleus branching with the body.

—(a) Infusoria in the widest sense: C. E. Ehrenberg. Die Infusionstierchen als vollkommene Organismen (1838); F. Dujardin, Zoophytes infusoires (1841). (b) Infusoria, including Mastigophora: M. Perty, Zur Kenntniss Kleinster Lebensformen (1852); E. Claparède and J. Lachmann, Études sur les infusoires