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, 
Fia. 60. 
Clio striata, removed from its shell, with 
the head above, right-side view. a, anus; 
a.g.g, accessory genital glands ; f, foot (pos- Fia. 61. 
terior lobe); ji, left fin (the right one is 
cut away); gg, gonad; h, heart; h.o, her- Veliger of Holis (Galvina) picta, 
maphrodite orifice ; k, kidney ; li, liver; m, ventral view. «a, anus; e, right 
mouth ; m.o, male orifice; m.p, mastica- eye; f, foot; in, intestine; ik, 
tory stomachal plate; n.s, central nervous kidney ; U.li, left liver lobe; m, 
system ; oe, oesophagus ; pa.c, pallial cavity ; mouth ; op, operculum ; of, right 
pa.g, pallial gland ; pe, penis; spo, sperm- otocyst; pa.c, pallial cavity ; 7.1i, 
oviduct ; st, stomach and bile-duct; t, right right liver lobe; 7.mu, retractor 
tentacle. muscle; st, stomach ; ve, velum. 
one on either side of the rectum, in various Rhipidoglossa, such as 
Plewrotomaria (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. 
