. Elementary text-book of zoology. Zoology. Cb so that the ciliated embryo still enclosed in the egg membranes repre- sents a small colony of two individuals. In the marine chilostomatous Bryozoa the fertilized egg passes into the ovicell, which consists of a helmet-shaped capsule and a vesicular operculum. Here the egg segments and develops into an embryo, which passes out as a ciliated larva, and swims about freely in the sea. The irregularly globular larva possesses a ring of cilia (fig. 550, a, b, c). After some time the larva attaches itself and develops the tentacular crown. The primary
. Elementary text-book of zoology. Zoology. Cb so that the ciliated embryo still enclosed in the egg membranes repre- sents a small colony of two individuals. In the marine chilostomatous Bryozoa the fertilized egg passes into the ovicell, which consists of a helmet-shaped capsule and a vesicular operculum. Here the egg segments and develops into an embryo, which passes out as a ciliated larva, and swims about freely in the sea. The irregularly globular larva possesses a ring of cilia (fig. 550, a, b, c). After some time the larva attaches itself and develops the tentacular crown. The primary zooeciuni soon produces new zooecia by budding ; avicularia are developed, and final- ly, but not until after the death of the old- er zooecia, root fila- ments. In the Endoprocta the egg develops in a brood-pouch placed on the oral side of the animal. The segmentation is complete, and leads to the formation of a blasto- sphere ; the endoderm arises by invagina- tion, and gives rise to the lining of the midgut ; the oesophagus and rectum being formed from the ectoderm t'fig. 551). The mesoderm arises from two cells. The larvse of the Endoprocta possess an alimentary J canal bent into the form of a horse-shoe, and a cilkted coikr which is prot™ded at the front end; further, they contain a bud (fig. 551 e, Kn}, as the first rudiment of a second individual, and a cement gland at the hind end (Dr). Other larval forms, which are apparently of a very different 'structure, are reducible to the same type — , Cyphonautes (fig. 500, c), a larva which is found in all seas, and is, according to Schneider, the larva of Membranipora pilosa. After the winter the contents of the statoblasts give rise to simple, non-ciliated animals, which possess, when they are hatched, all the parts of the adult animal, at once become attached, and produce new colonies by (after Barrois). b, Larva of Le- in-<ii, a (after Barrois). c, anus; cb, tuft of cilia; KH,. Please note that these im
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
