XII 



PHYLUM MOLLUSCA 



743 



In the limpets (Patella and its allies, Fig. 633) the true 

 ctenidia are represented only by a pair of vestiges, and respiration 



s/i 



a-' 



Fio. r,32. Pleurophyllidia-lineata , 



from the ventral surface, a. anus ; 

 l>r. secondary branchiae : /. mouth ; 

 s. o. sexual opening. (From the C'am- 

 Iriilge Natural Histori/.) 



Fio.j633. Patella vulgata,iseenjfrom theven 

 tral side. /. foot ; g. I. circlet of gill-lamellje ; 

 m. f. edge of the mantle; mu. attachment-muscle; 

 si. slits in the attachment-muscle ; sh. shell ; 

 '-. efferent branchial vessel ; '. aorta ; re. smaller 

 vessels. (From the Cambrulcie Natural History.) 



pit,} ap 



is carried on by a number of secondary branchise (g. I.) in the form 

 of lamellae situated between the short lateral fold of the mantle and 

 the foot. In the Pulmonata, and in some members of other groups, 

 ctenidia are absent, ' put v 



and the mantle- 

 cavity, completely 

 enclosed except for 

 a small rounded 

 opening, has the 

 function of a pul- 

 monary sac or lung 

 (Fig. 634), its roof 

 being richly supplied 

 with blood-vessels : 

 in the aquatic forms 

 its function is ap- 

 parently as much 

 hydrostatic as re- 

 spiratory. In one 

 family of Pulmonata, 

 the pulmonary chamber gives off a number of branching air-tubes 

 or trachece. In some of the Pulmonata there is a return to 



reel 



7i r 



ctorl 



wte.ph 



Fir,. 634. Pulmonary cavity and related parts in a slug 

 (Xiimax). aort. aorta ; aur. auricle ; neph. nephridium ; 

 peric. pericardium, laid open ; puL ap. pulmonary aperture ; 

 pul. r. pulmonary vein with its ramifications ; rect. rectum ; 

 ur. ureter ; vent. Ventricle. (After Pelseneer.) 



