358 INVERTEBRATE MORPHOLOGY. 



gas. The centre of each partition is perforated, arid through 

 the opening there extends to the tip of the shell a prolongation 

 of the body of the animal, termed the sipuncle. 



The foot of Nautilus, or at least that portion of it which 

 fuses with the head, has already been described as forming a 

 number of tentaculiferous lobes. These lobes are arranged 

 in the female in two series- one ventral, consisting of three 



FIG. 159. Nautilus pompilius, FEMALE. WITH THE SHELL SECTIONED LONGI- 

 TUDINALLY TO SHOW ITS INTERNAL STRUCTURE (after LECNIS from HKRTWIG). 



1 = mantle. 7 = uidameutal gland. 



2 = dorsal lobe of mantle. 8 = shell-muscle. 



3 = tentacles. 9 = terminal chamber of shell. 



4 = head-cap. 10 = partitions between the various 



5 = eye. chambers. 



6 = funnel. 11 -= sipuucle. 



lobes which immediately abut upon the mouth, and a more 

 dorsal riuglike lobe the anterior portion of which is de- 

 veloped into a hood (4) which arches over and protects the re- 

 tracted tentacles. Around the margins of both the ventral 

 and dorsal lobes are arranged the tentacles, each of which 

 is filiform and capable of being withdrawn into the basal por- 

 tion, which thus serves as a sheath. In addition to these 

 tentacles two other tentacles are found in close proximity to 

 the eye, one being on its ventral side and the other on its 

 dorsal. In the male the arrangement is very similar, except 

 that the median lobe of the ventral series is transformed into 

 a lamellated structure and does not bear tentacles, while a 

 portion of each of the lateral lobes of the inner series is sepa- 



