3. so 



MOLL use A. 



The foregoing description applies to but part of the Cephalop- 

 oda. Tlie highly different Nautilidas have a large number of 

 lolje-like processes on the head, these without suckers. The eyes 

 are deep pits, opening to the exterior by a small aperture, the base 

 of the x'it being occupied hy the retina, while lens, vifreous body, 

 iris, and (cornea are lacking (tig. .384). It is to Iju noticed that the 

 other cephalopod eyes pass through a NautiluH stage. 



In the trunk anterior and loosterior sides are distinguishable, 

 the two 2)assing into each (jtlier on the sides. The anterior side 

 (which corresponds only in part to the ventral side of other mol- 

 luscs) is wholly covered by the mantle, a strong muscular fold, 

 which takes its origin from the peri^jhery of the body, often 

 encroaching upon the back and always terminating with free mar- 

 gins at the head. 0)i opening the mantle by a ventral incision (fig. 

 385) the two cteuidia (four in Xnvfilus) are seen on either side. 



Fro. ^S5. — sV/wVf nffidufillti^ the mantle and left nephridlal sac opened to show the 

 vena cava leading to the branchial heart. <i,anns; h. il. lock of siphon and mantle; 

 r/, genital opening; A', licad: k, cicnidinm ; ti. nephridlal sac ; n'. nephridial open- 

 ing ; sp^ neiihrostonie ; /, inlv sac ; 7V, siphon. 



r)ctw(!en tliein in the middle line is the anus, and right and left 

 <if this and a little l)ehind ai'e the neiihridial 0])cnings (four in jVau- 

 liJnfi, which also has osfihradia). 'More laterallv are the sexual 

 openings, of which one (usually the right) is commonly absent. 



