'24 



ZOOLOGY 



Fio. 610. — Operculum of 

 Triton nodiferus. 



muscle (Fig. 611, col. m.) — which extends from the concave right 

 side of the animal to the columella, into which it is inserted; it 

 is by means of this muscle that the anterior portion of the body, 

 capable of being thrust out through the 

 mouth of the shell, may again be with- 

 drawn. 



If the Triton be examined in the ex- 

 tended condition (Fig. 611) it will be 

 found to present a distinct head, which 

 bears dorsally a pair of appendages — the 

 tentacles (tent) — of a sub-cylindrical shape, 

 slightly compressed towards their bases, and narrowing some- 

 what towards their free extremities ; these are capable of being 

 extended -and contracted, but not of being completely retracted. 

 Each bears on its outer side, some little distance from the base 

 a prominent eye. At the anterior end of the head on its ventral 

 aspect is the opening of the mouth. When the animal is 

 feeding, an elongated cylindrical introvert (Fig. 612), comparable 

 to that of Sipunculus (p. 492), is extended forwards, bearing 

 the mouth at its anterior end; at other times the introvert is 

 completely involuted within the head and anterior portion of 

 the body. In the male, on the right-hand side of the body some 

 little distance behind the head, is a long, narrow fleshy process, 

 broader at the base than at the free end, and deeply grooved 

 longitudinally ; this is the penis. Running back from its base 



manlcav co u 



tent 



frve.ta.fid rnesopct 



Fio. Oil.— Lateral view of the body of a female specimen of Triton nodiferus, removed from 

 the shell, moderately extended, col. m. columellar muscle ; coll. collar of mantle ; eye, eye ; 

 liv. liver ; mant. car. mantle-cavity ; meso. mesopodium ; neph. nephridium ; op. operculum ; 

 M>. ovary ; prop, propodium ; atom, stomach ; tent, tentacles 



is a narrow grove with prominent lips — the sperm-groove, con- 

 tinuous with that of the penis; in the female these parts are 

 not represented. 



Foot. — On the side of the body (ventral) which the animal 

 applies to the surface of the ground when it extends from the 

 shell is a flat surface elongated in the antero-posterior direction. 



