. The microscope and its revelations. studied, when mounted as pre-parations, even better than when alive. The larval zijoids have, bysecondary adaptations to their mode of life, acquired a type quitedifferent from that which characterises the adults; for instead of ,-iradial symmetry they exhibit a Itifatfral, the two sides being pre-cisely alike, and each having a ciliated fringe along the greater partor the whole of its length. Thetwo fringes are united by asuperior and an inferior trans-verse ciliated band, and be-tween these two the mouth ofthe zboid is always external forms
. The microscope and its revelations. studied, when mounted as pre-parations, even better than when alive. The larval zijoids have, bysecondary adaptations to their mode of life, acquired a type quitedifferent from that which characterises the adults; for instead of ,-iradial symmetry they exhibit a Itifatfral, the two sides being pre-cisely alike, and each having a ciliated fringe along the greater partor the whole of its length. Thetwo fringes are united by asuperior and an inferior trans-verse ciliated band, and be-tween these two the mouth ofthe zboid is always external forms of theselarva?, however, vary in a mostremarkable degree, owing to theunequal evolution of their dif-ferent parts; and there is alsoa considerable diversity in theseveral orders as to the propor-tion of the fabric of the larvawhich enters into the compo-sition of the adult form. Whenthe young begins to acquire thecharacters of the fully developedstar-fish and sea-urchin, theparts which are not retainedshrivel up, and their substance. goes to feed the young form. FIG. 683.—JBipiitiinriti <mt< i-ii/rm, or larvaof star-fish : (/, mouth; a, oesophagus; b,intestinal tube and anal orifice; <••, furrowin which the mouth is situated ; d , 7, ciliatedarms. One of the most remarkableforms of Echinoderm larva? isthat which has received thename of Bipinnarla (fig. 688).from the symmetrical arrange-ment of its natatory organs. The mouth (<(). which opens in themiddle of a transverse furrow, leads through an oesophagus, «, to alarge stomach, around which the body of a star-fish is developingitself; and on one side of this mouth are observed the intestinaltube and anus (b). On either side of the anterior portion of thebody are six or more narrow fin-like appendages, which are fringedwith cilia; and the posterior part of the body is prolonged intoa sort of pedicle, bilobed towards its extremity, which also iscovered with cilia. The organisation of this larva seems
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
