. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 440 jaws can be distinguished from the region of the body, (thorax) bearing the biramous appendages, but there is no distinct boundary between these two regions. The anus is situated at the extremity of the small stump-like abdomen, which succeeds the thorax and is often only indicated by two caudal appendages. Posterior antennae are in- variably absent, while the anterior pair persists, even in the adult, as small organs of attachment. The oral apparatus is situated on a ventral prominence of the c
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 440 jaws can be distinguished from the region of the body, (thorax) bearing the biramous appendages, but there is no distinct boundary between these two regions. The anus is situated at the extremity of the small stump-like abdomen, which succeeds the thorax and is often only indicated by two caudal appendages. Posterior antennae are in- variably absent, while the anterior pair persists, even in the adult, as small organs of attachment. The oral apparatus is situated on a ventral prominence of the cephalic region, and consists of an upper lip with palps, two mandibles and four maxillae, of which the two last unite to form a sort of under lip. On the thorax there are usually six pairs of many-jointed biramous appendages, the elongated cirriform rami of which are richly beset with hairs and setae and serve to set up currents in the water in which the particles of food are brought to the animal. The stump-shaped abdomen bears an elongated cirrus, which is bent to- wards the ventral surface between the thoracic appendages, and con- stitutes the male copulatory organ. There are numerous and very pecu- liar variations in the shape of the whole body. Not only may the de- position of calcareous matter in the mantle be wanting, and the bira- mous thoracic appendages be reduced in number or even absent, but the mouth parts and the appendages may also be lost {Peltogastridoe), and the body may be reduced to the form of an unsegmented tube, sac, or lobed disc. Nervous system and sense organs.—The Cirripedia possess a paired cerebral ganglion and a ventral chain of ganglia, of which there are usually five paii-s, but which are sometimes fused to a common ganglion mass (Balanidce). There is a double eye, which, although rudimentary, corresponds to the unpaired Nauplius eye. An alimentary canal is absent only in the Rhizocephala. In the. Fio. 319.—The organization of Lepat, after re
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
