. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). N 660 IN VERTEBRA TE MOltPIIOLOG Y. % terior extremity, forruing a postoral ciliated band, the anus lying without the area enclosed by it. In front of the mouth is a trilobed region also surrounded by a band of cilia, the adoral band. -In young embryos the adoral and postoral bands are united at the apex, separation only super- vening later. In later stages two additional arms jire developed at the sides of the apical lobe, wliich becomes like the new arms destitute of
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). N 660 IN VERTEBRA TE MOltPIIOLOG Y. % terior extremity, forruing a postoral ciliated band, the anus lying without the area enclosed by it. In front of the mouth is a trilobed region also surrounded by a band of cilia, the adoral band. -In young embryos the adoral and postoral bands are united at the apex, separation only super- vening later. In later stages two additional arms jire developed at the sides of the apical lobe, wliich becomes like the new arms destitute of cilia, and tipped with a group of wartlike elevations. This form of the larva is kno'.vn as tlie Brachiolaria. A peculiar process, amounting almost to a metamorphosis, occurs during the transformation of the larva into the Starfish. Calcareous plates of tlie aboral system make their appearance on the surface of the stomach. Fig. 256.—Bipinnarta op AsteraeantJiion (after agassiz). an = anus. fiy = liydrocoel. m = mouth. near the posterior end of the body, and oral plates on the ventrjil surface of the same organ. These two systems, at first rather widely separated, gradually approach each other, and at the same time the internal organs assume the adult form. Finally the two series of plates unite, enclosing between them the hydrocoel, a portion of the digestive tract and of tlie coe- lom. The original mouth and anus are obliterated, and indeed the anter- ior half of the larva takes no part in the formation of the adult animal, but is gradually absorbed. A highly-developed faculty for regeneration occurs in the Asteroidca, the disk being able to regenerate lost arms; and indeed an arm, with which a small fragment of the disk is in connection, has the power of regenerat- ing all the missing parts. Specimens of tlie common Starfish Asterias are in consequence frequently found with one or more of the arms bifid at the tip, or even with an abnormal number of Please
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1894
