. A manual of zoology. Zoology. 248 CaiLENTERATA. ;ixis and an outer layer of ectoderm. The entoderm forms an otolith sac at the tip, while the ectoderm furnishes a nervous cushion of ganglion cells and fibres and usually a simple e)'e spot. Less evident is the effect of the lobing on the internal organs. The gastrovascular system begins with a quadrate or X-shai:)ed mouth (fig. 193). The perradial angles of the mouth are usually produced into long curtain-like oral tentacles of great use in the capture of food. The ' stomach,' \yhich begins just inside the mouth, gives ofE four interradial (i
. A manual of zoology. Zoology. 248 CaiLENTERATA. ;ixis and an outer layer of ectoderm. The entoderm forms an otolith sac at the tip, while the ectoderm furnishes a nervous cushion of ganglion cells and fibres and usually a simple e)'e spot. Less evident is the effect of the lobing on the internal organs. The gastrovascular system begins with a quadrate or X-shai:)ed mouth (fig. 193). The perradial angles of the mouth are usually produced into long curtain-like oral tentacles of great use in the capture of food. The ' stomach,' \yhich begins just inside the mouth, gives ofE four interradial (, alternating with the corners of the mouth). Fig. —Sense organs of Aurelia aurita. (After Schewiakoff.) cc, ectoderm; en, entoderm; qv, gastrovascular space ; m, supporting layer ; n, cup eye ; nc, pigment eye ; t)t, otolith sac ; ify, olfactory groove. pouches, the gastrogenital pockets. The epitlielium of these pouches produces on the one hand a group of small gastral tentacles (phacellas), each extremely mobile and supported bv an axis of mesoglcea; on the other jilaited folds of the gonads, these being, in contrast to the Ilydrozoa, of entodermal origin. In this the Scyphomeduspe show relationships to the Authozoa. From the central digestive sac arise the peripheral portions. These consist in the larval medusie (Ephyra stage, fig. 192) of eight radial canals to the sensory pedicels, and in most adult medusa? of these same pouches and eight others, adradial in position, to the tentacles. In some this primitive arrangement is complicated by an extensive network of tubes (fig. 193). In the species \\ith an alternation of generations the egg pro- duces a ciliated larva (fig. 19(1) which attaches itself and develops into a scyphostoma. This scyphostoma is alwa^'s capable of ter-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
