160 THE GASTROPODA 
hermophrodite with separate male and female gonads ; parasitic in the 
testis of Holothurians, causing their abortion. Three species are 
known: one in Synapta digitata (Mediterranean), one in Holothuria 
edulis (Philippines), and one in a Holothuria from Puget Sound in the 
North-East Pacific. Hnteroxenos, Bonnevie ; no pseudopallium and no 
alimentary tract; male and female gonads separate, with a single 
common genital orifice; larvae operculiferous. . ostergreni (Fig. 
140); parasitic in the intestine of 
Stichopus (Norway). 
Fic. 139. 
Entoconcha mirabilis, in situ, mag- 
nified. I, oral extremity ; IL, remains 
of the digestive tract ; III, testis; IV, oe 
t : 3 : Fic, 140. 
ovary; V, antimesenteric vessel of ; f 
the Synapta in which ELntoconcha is Enteroxenos ostergreni, Bonnevie. 
parasite. (After J. Miiller.) ov, eggs. (After Bonnevie.) 
TRIBE 2. HETEROPODA. 
These are free-swimming Taenioglossa, with the foot flattened 
laterally and the otocysts situated near the cerebral ganglia. There 
are no mandibles and the intestine is short. All the Heteropoda are 
pelagic, and are much modified in adaptation to this mode of existence. 
The foot is very large, and has the form of a fin compressed bilaterally ; 
it bears, in the male at least, a sucker on its ventral aspect (Fig. 142, d’). 
The visceral sac or “nucleus” and mantle form a progressively smaller 
and smaller part of the mass of the body (compare Figs. 142 and 143), 
but the head always remains large and forms a cylindrical snout. The 
cerebral nerve-centres are in juxtaposition; the pleural ganglia, still 
visible in the Atlantidae and Pterotracheidae, are attached to them, and 
there are thus two pedal connectives on either side, namely, the cerebro- 
pedal and the pleuro-pedal ; these are separate proximally in Atlanta, but 
is 
