. Outlines of zoology. al groove,with a radula bearing one tooth, witha distinct digestive gland, and withtwo nephridia opening separately intoa posterior cavity, which also containstwo gills. The sexes are separate. Class III. SCAPHOPODA Very different in many respects fromGasteropoda are the Scaphopoda, ofwhich Dentalium (Elephants tooth-shell) is the commonest genus. Theyare apparently related to the Zeugo-branchiate Gasteropods, and also tothe simplest Bivalves. They burrowin the sand at considerable depth offthe coasts of many countries. Themantle has originally two folds, whichfuse ventr
. Outlines of zoology. al groove,with a radula bearing one tooth, witha distinct digestive gland, and withtwo nephridia opening separately intoa posterior cavity, which also containstwo gills. The sexes are separate. Class III. SCAPHOPODA Very different in many respects fromGasteropoda are the Scaphopoda, ofwhich Dentalium (Elephants tooth-shell) is the commonest genus. Theyare apparently related to the Zeugo-branchiate Gasteropods, and also tothe simplest Bivalves. They burrowin the sand at considerable depth offthe coasts of many countries. Themantle has originally two folds, whichfuse ventrally, and the shell becomescylindrical, like an elephants is open at both ends. The largeropening (directed downwards in thesand) is anterior, the concave side ofthe shell is dorsal. The mouth opensat the end of a short buccal tube,at the base of which is a circle ofciliated tentacles. The foot is long,with three small terminal lobes. Itis used in slow creeping, and is pro-There are cerebral and pleural ganglia. Fig. 231.—Proneomenia. Ner-vous system.—From Hubrecht. eg;., Cerebral ganglia; sig., sublingual;^ anterior pedal; p.^.£.^ pos-terior pedal; i>. posterior vis-cerals : sl.^ sublingual connectives ;cpc.^ cerebro-pedal connective ; pe.^longitudinal pedal nerves ; la., long-itudinal lateral nerves. truded at the anterior opening. near one another in the head, pedal ganglia in the foot, and a longuntwisted visceral loop with olfactory ganglia near the posterior organs are represented by otocysts beside the pedal is an odontophore with a simple radula. The food consists ofminute animals. There is a much reduced heart, and colourless bloodcirculates in the body cavity. There are two nephridial apertures, pne LAMELLIBRANCHIATA. 425 on each side of the anus ; and two nephridia. The sexes are separate ;the reproductive organ is simple and dorsal in position; the elementspass out by the right nephridium. The gastrula is succeeded
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
