i 9 8 



THE SCAPHOPODA 



orifice of the shell and subjacent mantle is morphologically the 

 anterior or cephalo-pedal aperture. Near the smaller posterior 

 aperture the shell, being older, is also thicker. The anterior 

 aperture of the mantle has a conspicuously thick border. The 

 posterior aperture is emarginated by a ventral sinus and is furnished 

 interiorly with a dorsal and a ventral valve, which are capable of 

 being applied to one another. The animal lives buried obliquely 

 in the sand, only the posterior extremity projecting into the water, 

 and therefore it is the posterior aperture that is at once inhalant 

 and exhalant and serves for the expulsion of the excrements and 



A or 



Fin. 181. 



Dentalium vnh/are. A, ventral view of the animal removed from its sholl ; R, dorsal view of 

 the same ; C, right-side view of the same ; D, the shell in section ; E, right-side view of the 

 animal in its shell, with cephalic appendages (captacula) exserted as in life. , mantle ; a', 

 longitudinal retractor muscle ; a", fringe surrounding the anterior opening of the mantle- 

 chamber ; a'", the posterior appendix of the mantle ; ?>, anterior circular muscle of the mantle ; 

 V, posterior circular muscle of the mantle ; c, c', longitudinal retractor muscle ; c, liver ; /, 

 gonad ; k, buccal mass (seen through the mantle) ; <i, left kidney ; s', anterior extremity of the 

 foot ; w, w 1 , longitudinal blood-sinus of the mantle. (From Lankester, after Ijacaze-Duthiers.) 



the genital products. In the extended state of the animal the foot 

 and cephalic tentacular filaments project from the anterior opening. 



The pallial cavity extends continuously from one aperture to 

 the other. In the middle and posterior regions of the body the 

 liver, the gonads, and even the kidneys, extend into the mantle and 

 may increase its thickness to such an extent that the pallial cavity 

 is reduced to a rather narrow canal (Siphonopodidae). 



The head is situated at the anterior end of the body on the 

 concave or dorsal side. In shape it is a sort of cylindrical 

 projection or proboscis, and is contractile but not invaginable. In 

 the Dentaliidae its anterior aperture is surrounded by eight palps 

 or lobes with scalloped margins, but in the Siphonopodidae it is 



