. Elementary text-book of zoology. Zoology. the stage with four segments, the segments are so disposed that two perpendicular planes placed between them would correspond to the two principal planes of the fully developed animal. Each of the four spheres gives rise to one of the four quadrants of the adult animal (Fol.) The whole mass of the finely granular exoplasm now becomes collected at the upper end of the segmentation spheres, where it is separated off and gives rise to eight ne\v small spheres. These, by continued division, break up into a great number of small nucleated ce
. Elementary text-book of zoology. Zoology. the stage with four segments, the segments are so disposed that two perpendicular planes placed between them would correspond to the two principal planes of the fully developed animal. Each of the four spheres gives rise to one of the four quadrants of the adult animal (Fol.) The whole mass of the finely granular exoplasm now becomes collected at the upper end of the segmentation spheres, where it is separated off and gives rise to eight ne\v small spheres. These, by continued division, break up into a great number of small nucleated cells, which increase rapidly and gvow round the eight large seg- mentation spheres or the cells produced from them. The young Ctenophorn sooner or later leave the egg membranes, and at this period differ more or less from the sexually mature animal in the simpler and usually more spherical form of the body, in the small size of the tentacles and swimming plates, and in the differ- ence in the relative size of the oesophageal tube, infuiidibulum, and vascular canals. The differences are most striking in the lobed Gtmoplwra (with the exception of Cestuiii), the embrj'os of which have a great similarity to the young of Ci/, and have no traces of bi-radial structure. It is only after a, longer period of larval life that the completely mature form is attained by the unequal growth of the swimming plates and their canals, the out- growth of the tentacle-like processes, and the formation of two lobe-like projections round the mouth from those halves of the body which correspond to the longer rows of swimming plates. The phenomenon remarked by Chun is worthy of notice, that the young of Eii-ch<tr'o*, while still in the larval stage, become sexually mature during the hot period of The Ctenophora live in the warmer seas, and, under favourable conditions, often appear in great quantities at the surface. They feed OH marine animals of various size, which they capture with their
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
