59 



w. The pupil. 

 X. X. X. The partitions of the chambers. 

 y. y. y. The septal tubes which give passage to the membranous siphon. 



z. The chamber of occupation. 



PLATE II. 



Figure 1. Nautilus Pompilius, in the prone position, with the orifice of the 

 oral sheath enlarged to expose the labial processes and tentacles surrounding 

 the mouth. 



a. The mantle. 



b. Its dorsal fold coUapsed. 



c. Its anterior margin. 



d. The process of the mantle which separates the funnel from the head. 

 e. e. Tlie convexities produced by the ovarian gland. 



/. The orifice of the funnel a little widened ; the funnel itself is drawn 

 down to show the surface of the oral sheath on which it rests. 

 g. g. The levatores infundibuli exposed by laying open the canals in which they 

 were concealed. 

 h. The hood. 



i. Its superior plane surface longitudinally divided. 

 k. h. The cut-surfaces. 



I. The smooth internal surface of the oral sheath. 

 m. m. The digitations, showing their orifices, the tentacles being retracted. 

 (The entire number is given on the right side.) 

 m. The large papillose digitation. 

 n. The inferior parietes of the oral sheath. 

 0. 0. Tlie external labial processes. 

 p. p. The internal labial processes.- 



q. The convex outer surface of the organ of smell, 

 r. r. The labial tentacles. 

 s. One of the ophthalmic tentacles. 

 t. The eye. 

 M. The inferior ridge. 



I 2 



