THE GASTROPODA 



79 



be noted that in those Euthyneura which are detorted in the adult 

 condition, the primitive torsion is manifest in the course of develop- 

 ment, and in the larvae the pallial cavity is anterior and dorsal, the 



anus anterior, just as is the 

 case in an adult Streptoneura 

 (Fig. 61). 



The pallial cavity normally 

 contains the apertures of the 

 anus and the renal ducts ; and, 

 as it also contains the ctenidial 

 branchiae, together with their 

 sensory organ, the osphradium, 

 it constitutes the respiratory 

 cavity. There is, in addition, 

 between each branchia and the 

 rectum a more or less dif- 

 ferentiated glandular region 

 known as the hypobranchial 

 gland or pallial mucous gland 

 (Figs. 75 and 85), which is 

 characteristic of aquatic species. 

 Two such glands are found, 



m 



FIG. GO. 



Clio striata, removed from its shell, with 

 the head above, right-side view, a, anus ; 

 a. g.g, accessory genital glands ; /, foot (pos- 

 terior lobe); fi, left fln (the right one is 

 cut away) ; gg, gonad ; h, heart ; h.o, her- 

 maphrodite orifice ; k, kidney ; li, liver ; m, 

 mouth ; m.o, male orifice ; m.p, mastica- 

 tory stomachal plate ; n.s, central nervous 

 system ; oe, oesophagus ; pa.c, pallial cavity ; 

 pa.g, pallial gland ; pe, penis ; spo, sperm- 

 oviduct ; st, stomach and bile-duct ; (, right 

 tentacle. 



Fio. 61. 



Veliger of Eolis (Galvina) picta, 

 ventral view, a, anus ; e, right 

 eye ; /, foot ; in, intestine ; k, 

 kidney; l.li, left liver lobe; m, 

 mouth ; op, operculum ; ot, right 

 otocyst ; pa.c, pallial cavity ; r.li, 

 right liver lobe ; r.mu, retractor 

 muscle ; st, stomach ; ve, velum. 



one on either side of the rectum, in various Rhipidoglossa, such as 

 Pleurotomaria (Fig. 127), Haliotis, Turbo, etc., but only one, namely, 

 that of the left side, in the majority of aquatic Gastropods with a 

 well -developed mantle. . This glandular organ becomes median 

 and nearly symmetrical in the Cavoliniidae (Fig. 60) and the 

 Cymbuliidae. 



