Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 252 COiLENTEEATA. relatively long tongue-like processes, and grow out from the disc-like segments of the Strob'da as marginal cones. An undivided mar- ginal membrane (the velarium), differing from the velum of the Craspedota [in containing prolongations of the canals of the gastro- vascular system], is present in the Charyhdeidce alone. The Acalejiha differ from i\xQ IIjdromedusce in possessing, as a rule, large oral tentacles at the free end of the wide manubrium. These may
Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 252 COiLENTEEATA. relatively long tongue-like processes, and grow out from the disc-like segments of the Strob'da as marginal cones. An undivided mar- ginal membrane (the velarium), differing from the velum of the Craspedota [in containing prolongations of the canals of the gastro- vascular system], is present in the Charyhdeidce alone. The Acalejiha differ from i\xQ IIjdromedusce in possessing, as a rule, large oral tentacles at the free end of the wide manubrium. These may be regarded as being derived from an unequal growth of the edges of the mouth. They grow as four arm-like processes of the manubrium from the angles of the mouth, and are placed radially, Fig. 195.—Diagrammatic lons-itudinal section through a lihizafoma. U, Umbrella; 3T, gastric cavity; S, sub-umbrella; G, genital band; Sih, sub-genital pit; F, filament; SUf, muscle system of the sub-umbrella; Ji,//, radial vessels; Hk, sense Grfjars; JRg, olfactory pits; Al, ocular lobe; Sir, shoulder tufts; Dk, dorsal tufts; I't, ventral tufts of the eight arms ; Z, terminal parts of the arms. they alternate with the genital organs and gastric filaments. In some cases the arms become forked at an early period, and four pairs of arms are formed, the lobed tufted edges of which may again divide and sub-divide into many branches. In this case, the margins of the mouth and the opposed surfaces of each pair of arms fuse in early life in such a way that the original central mouth becomes obliterated, and in its place there are developed a number of .small tufted orifices on the peripheral parts of the arms, through which nutriment is taken in (Rhizostomido'. fig. 195).
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