XII 



PHYLUM MOLLUSCA 



723 



is, as in Triton, only a single row of filaments retained, and the 

 organ is attached throughout its length. 



fi- 



7.1 



sh 



Tn.e 



n 



JiU 



,-br 



a 



;. Hi:;. rieurophylliclia lincata, 

 from the ventral surface, a. anus ; 

 br. secondary branchiae : m. mouth ; 

 s. o. sexual opening. (From the Cam- 

 bridge Natural History.) 



FIG. C43. Patella vulgata, seen from the 

 ventral side. /. foot ; g. I. circlet of gill- 

 lamellse ; m. e. edge of the mantle ; mu. attach- 

 ment-muscle -. si. slits in the attachment- 

 muscle ; sh. shell ; v. efferent branchial vessel ; 

 o' ' . aorta ; ve. smaller vessels. (From the Cam- 

 bridge Natural History.) 



j 







/ \ 



put ap 



reel 



In the Nudibranchs true ctenidia are absent, but their place 

 as breathing organs is taken by a number of secondary branchice, 



sometimes simple, 

 sometimes branched 

 or pinnate processes, 

 which are distributed 

 over the dorsal sur- 

 face, as in Eolis ; or, 

 as in Doris (Fig. 633), 

 form a circlet sur- 

 rounding the anus ; or, 

 as in Pleurophyllidia 

 (Fig. 642), a row on 

 each side beneath the 

 mantle-flap. 



In the limpets 

 (Patella and its allies, 

 Fig. 643) the true 

 ctenidia are r e p r e - 

 sented only by a pair of vestiges, and respiration is carried 

 on by a number of secondary branchiae (g. I.) in the form of 

 lamellge situated between the short lateral fold of the mantle 



vent 



FIG. 



644. Pulmonary cavity and related parts in a 



aort. aorta ; aur. auricle ; neph. kidney 

 pc.ric. pericardium, laid open ; pul. ap. pulmonary aperture 

 puJ. v. pulmonary vein with its ramifications ; rect. wt HIM 

 ur. ureter ; vent, ventricle. (After Pelseneer.) 



