ON NAUTILUS AND SOME OTHER ORGANISMS. tat 
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Fic. 17.—N. pompilius, ¢. View of nuchal region, to further illustrate 
the circulus pallialis. The dorsal free mantle-edge is reflected and a median 
incision made. 4%. Hood. coz. Conecavity at base of hood, in which the 
nuchal membrane (z. m.) lies. f. Dorso-posterior portion of funnel. x. a. 
Nuchal artery. co/. Columellar muscle. m. p. a. Marginal pallial artery. 
p.m. a. Pallio-nuchal arteries. d.a. Dorsal aorta. m.e. Free mantle-edge. 
c. e. Cut edges of mantle and body-wall. 
N.B.—The dorsal aorta shapes its course in this region in accordance with 
the state of repletion of the erop. 
