. Animal biology. Zoology; Biology. 86 PROTOZOA tions of a nervous system; sensitive areas, which function as sense organs; and supporting parts, which form a sort of skeleton (Fig. 31). The food of protozoans consists of organic matter, both vegetable and animal, living and dead. Their metabolism is, in general, similar to that described for the ameba or the Paramecium. Because of the size of the animals the study of digestive enzymes is difficult, and there is little precise knowledge. Protozoans certainly digest proteins, have been shown to be able to use emulsified fats, and also are able
. Animal biology. Zoology; Biology. 86 PROTOZOA tions of a nervous system; sensitive areas, which function as sense organs; and supporting parts, which form a sort of skeleton (Fig. 31). The food of protozoans consists of organic matter, both vegetable and animal, living and dead. Their metabolism is, in general, similar to that described for the ameba or the Paramecium. Because of the size of the animals the study of digestive enzymes is difficult, and there is little precise knowledge. Protozoans certainly digest proteins, have been shown to be able to use emulsified fats, and also are able to use certain starches. In addition to fission, or binary division, and sporulation, protozoans sometimes exhibit a third type of asexual reproduction known as gemma- tion, or budding. In this case individuals of smaller size than the parent grow out from it like buds and when developed break loose, later growing to the same size as the individual which produced them (Fig. 32).. A B Fig. 32.—Gemmation, or budding, in Ephelota gemmipara (Hertwig). (After Hertwig, in Morphologisches Jahrhuch, vol. 1.) A, organism on stalk, showing two types of ten- tacles, suctorial and prehensile, the latter with spiral ridges on the surfaces. B, an indi- vidual showing the formation of buds, into each of which extends a portion of the nucleus. These buds become detached and free-swimming; they possess cilia on one side but later develop tentacles and become attached. X 120. 112. Sexual Reproduction in Protozoa.—Some colonial protozoans exhibit a simple form of sexual reproduction. The animals in the colony become divided into two types: the ordinary ones, known as nutritive individuals, or nutritive zooids, which reproduce by fission in the ordinary way; and a second type which is represented by reproductive individuals or gametes. These gametes exist in two forms: the larger macrogametes, which, like egg cells, are usually not active; and the smaller microgam- etes, which, like the sperm
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