288 Introduction to Animal Morphology. 



stretches forward, and ends anteriorly by being at- 

 tached by a globular, toothless portion (Orbis radulae) 

 to the floor of the pharynx. The teeth are of chitin 

 or conchiolin, with calcic phosphate, and are true 

 cuticular structures ; they vary in number from ten 

 (Pontolimax) to many thousands (Trochidse) ; their 

 forms and numbers are of taxonomic value.* The 

 radula is absent in Phyllirhoe, Tethys, &c., as are the 

 pharyngeal jaws in Aplysia, Tethys, &c. 



In Doris there is a prehensile collar of two arched lancet- 

 like conchiolin plates outside the buccal lips, covered with a 

 file-like surface of close groups of bifid pointed warts. Pon- 

 tolimax anil Klysia have a prehensile, eversible sac appended 

 to tin- urobranchus, Lobiger, Lopluu 



here are two such side punches in the buccal mass, 

 attached in front and free behind, having long, outwardly- 

 curved, slipper-sole-shaped, horny p! 



Into the mouth behin in front of the radula, open 



the ducts of the salivary glands, which are usually two long 

 (Athmtiiho, &c.), or short caeca (Carinaria, ^olis, &c.), some- 

 times branched (Lobiger, I.nph.. .virus, cVc.), sometimes 

 corkscrew-like (Voluta), or forked (Pleurophyllidia, &c.), very 

 rarely. In Tea bra and Polycera only a single follicle e 

 In Phyllidia two lateral and < >U8. In Pleurobranchus 



there are three long, branched caeca reaching to the liver. 



* The forms of radula are: I. Gymnoglossa toothless, as Acus. 

 2. Rachiglossata with only rachis plates, as Volutida?. 3. Hamiglossata 

 with r;ichi> pl;:tes and one row of lateral teeth (Murex, Buccinidoe, Ol 

 4. Toxoglossata with no rachis teeth, but an intermediate and a lateral 

 nuhv and Pleurotomidae). 5. Txnioglossata with one row of 

 rachis teeth and three lateral plates on each side (Strombidoe, Littorinida?, 

 Ccrithiadx, &c.) 6. Ptcnoglossata with no rachis teeth, and many lateral 

 (Scalaria, Janthina). 7. Rhipidoglossata with one rachis row, 4- 

 tcrmcdiatc and many small lateral rows (Xeritida?, Trochidae, Hah'-. 

 The paired jaws are also variable in Pulmonates, being absent (Agnatha), 

 with a sharp tooth (Oxygnatha), striped with a crenated edge (Aulaco- 

 gnatha), or with marginal rows of teeth (Odontognatha). 



