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SIPHUNCLE AND PALLIAL VESSELS. 



go far in one direction, but tended to move in circles, as they sometimes do without 

 severance of the siphuncle. If one of the individuals floating at the surface was forced 

 down to the bottom with a hand-net it would slowly rise to the surface again, as also 

 often happens with a Nautilus which has not been operated upon. Another specimen 

 showed the opposite tendency to sink to the bottom very gradually. 



Fig. 7. N. pompilius, s . View of nuchal region, to further illustrate the circulus pallialis. The dorsal free 

 mantle-edge is reflected and a median incision made. h. hood ; con. concavity at base of hood, in which 

 the nuchal membrane (n.m.) lies ; /. dorso-posterior portion of funnel ; n.a. nuchal artery ; col. columellar 

 muscle; m.p.a. marginal pallial artery; p.n.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 crop. 

 [From Quart. J. Micr. Sc. Vol. 39, 1896.] 



Some further features in the pallial circulation of Nautilus still remain to be 

 described before concluding this chapter. After successful injections a striking peculiarity 



