The porifera and coelentera . ore adaptable Choanoflagellata. Differences are seen chiefly in theposition of the nucleus, in the relative size, shape, and structure ofthe collar, and in the size of the cell as a whole. The largest collar cellsare founil in the Calcarea, and especially in the family Cluthrinidae, 54 SPONGES amongst which the species Ascundra falcata, H., is pre-eminent in thisrespect, and may be taken as a type (Fig. 52, A\ The cells in (questionare columnar, and about half as long apain as they are broad in thefully expanded state. When contracted they become narrower and more
The porifera and coelentera . ore adaptable Choanoflagellata. Differences are seen chiefly in theposition of the nucleus, in the relative size, shape, and structure ofthe collar, and in the size of the cell as a whole. The largest collar cellsare founil in the Calcarea, and especially in the family Cluthrinidae, 54 SPONGES amongst which the species Ascundra falcata, H., is pre-eminent in thisrespect, and may be taken as a type (Fig. 52, A\ The cells in (questionare columnar, and about half as long apain as they are broad in thefully expanded state. When contracted they become narrower and moreelongated, a change due to pressure of the surrounding tissues, and notprobably to the activity of the collar cells themselves (Fig. 52, i>, c). Thelarge nucleus is lodged at the base of the cell, as is always the casein Clathrinuiae, at least during the resting state of the cell. Eachchoanocyte is in contact with its neighbours fur about two-thirds of itslength, and the distal third forms a freely projecting neck {cAlum),. Collar cells of \-arious , fully expanded ; ?. !?•>?; -xj^ C. a. ?D, a, collar of HnlUgellum ; A, hoops s _and Pekelhariug. D, xluoO; a-c, x about &50 or 900. 52. A, oX Ascandrn falcata, H. /?, of Clathrina. ayriaetf, Mont. ; ??i . c. retracteil down to hoop: I. of complete •iliatum, Fabr. ; h, of / i, Mont. i, of :>pongilla ; he. hi- ; _/f, •I, nuclei. C, a, after Biii ? Vosmaer bearing the collar (coUatt). The junction of body and neck is marked bya distinct flange or shoulder. The base of the collar encloses a moundof protoj)lasm continuing the neck, from the centre of which arises thetlagellum. The cytoplasm has a very distinct alveolar or vacuolar structure, andlarger vacuoles—or it may be, one large vacuole—are commonly found atthe upper extremity, just below the tlagellum, representing very probablyfoixl vacuoles, by means of which the cell ingests food particles captureiiby the flagell
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
