. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 262 IN VERTEBRA TE MORPHOLOO Y. av mouths are concerned, and it is possible to divide the Gymno- Isemata into three groups or tribes, based upon these differ- ences. In the tribe Oydostomata the zooeeia are usually cylindrical, and the mouth is circular and destitute of any appendages ; in the Ctenodomata the mouth is closed during retraction by a series of bristles which surround it {Alcyonid- ium); Avhile in the ChUostomata, in which the ectocyst is. usually lirm and
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). 262 IN VERTEBRA TE MORPHOLOO Y. av mouths are concerned, and it is possible to divide the Gymno- Isemata into three groups or tribes, based upon these differ- ences. In the tribe Oydostomata the zooeeia are usually cylindrical, and the mouth is circular and destitute of any appendages ; in the Ctenodomata the mouth is closed during retraction by a series of bristles which surround it {Alcyonid- ium); Avhile in the ChUostomata, in which the ectocyst is. usually lirm and frequently calcified, the mouth is closed by a lid, the ojoc/'cm/mw, furnished with spe- cial muscles {Hugula, J/emhranipora). In this last-named tribe a poly- morphism of the individuals conipos- .. avi^n ^ colony is frequently found. Scattered among the ordinarj' indi- rm viduals others, the Avicularia (Fig. 116, av), may be found having fhe appearance of a bird's head, the lower beak being fastened to the head by a hinge and having inserted into it strong muscles ; bunches of sensory hairs are also ])resent, and when these are stimulated the lower beak is ra})idly snapped against the upper and the stimulating organism thus caught. There can be little doubt but that these Avicularia are specially modified individuals whose head and ujjper beak represent tiie ordinary iiidividnai, while the lower beak may ])i>ssibly be the equivalent of the operculum ; physiologically they liavc beeu usually regarded as specializ;d for the purj)()He of catching food for the ordinary individuals, but it is not improbable that their services may rather be of a cleansing nature, re- moving from the colony particles of dirt Hiid the extirota, which l)v accumulating might interferr' with the proper function of the tentacles. Another 00 _bb Fin. 118. —PouTioN OF Colony of Hugula. a = uinis. av = ftviculiida. bb = brown body. ee = ectofysl. / -- funiculus. oe = ovici'll. rf» = reUa(
Size: 995px × 2512px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishernewyo, bookyear1896
