CEPHALOPODA. 



419 



structure. The dorsal surface includes the visceral sac; roughly 

 the apex of the visceral sac may be regarded as the middle of 

 the dorsal surface. The anterior end is that surface of the head on 

 the sides of which the eyes are placed; while the posterior end 

 may be said to be marked by the anus. Inasmuch as the vis- 

 ceral sac is normally carried horizontally, the words " upper " and 



FIG. 334. Loligo vulgaris (from Lang, after D'Orbigny). A, from the posterior side, showing 

 the funnel just in front of the free edge of the mantle. H, from the front side showing the 

 eyes on the head. There are also shown the ten arms, the fins, and the chromatophores in 

 the skin. 



"lower" are sometimes used in the sense of "anterior-dorsal" and 

 "posterior-ventral" respectively; further, inasmuch as the visceral 

 hump is sometimes shown in figures in its proper morphological 

 position, as standing straight up above the head, the words upper 

 and lower are sometimes used in the sense of dorsal and ventral. 



