N A U 



Nummulites, Polystomella, Side- 

 rolites, and Verticialis. 



NAUTI'LIDJB. A family of chambered 

 shells belonging to the order Tetra- 

 branchiata ; of this family the 

 nautilus is a genus. 



NAU'TILITE. A fossil nautilus. 



NATJ'TILFS. A genus of shells belong- 

 ing to the family Nautilida3. A 

 spiral, polythalamous, discoidal 

 univalve with smooth sides. The 

 turns contiguous, the outer side 

 covering the inner. The chambers 

 separated by transverse septa, 

 which are concave outwards, and 

 perforated by a tube passing through 

 the disk. Three or four recent 

 species are known. " It is a curious 

 fact," says Dean Buckland, "that 

 although the shells of the nautilus 

 have been familiar to naturalists, 

 from the days of Aristotle, and 

 abound in every collection, the only 

 authentic account of the animals 

 inhabiting them, is that by Rum- 

 phius, in his history of Amboyna." 

 At the present day the nautilus is 

 an inhabitant of tropical seas, but 

 its fossil remains are found in for- 

 mations of every age. The organ 

 of locomotion in the nautilus appears 

 to have been a foot, resembling that 

 of the snail. This organ is ex- 

 pansive, and surmounts the head. 

 The oral organs are much more 

 complicated and numerous than 

 those of the cuttle-fish, and are 

 furnished with no suckers. Its 

 tentacles are retractile within four 

 processes, each pierced by twelve 

 canals protruding an equal number 

 of these organs, so that, in all, there 

 are forty-eight. In fact, the whole 

 oral apparatus, except the mandi- 

 bles and the lip, is formed upon a 

 plan different from that of the 

 cuttle-fish, as likewise from that of 

 the carnivorous trachelipod mollus- 

 cans, and indicate very different 

 modes of entrapping and catching 

 their prey ; being deprived of suck- 

 ers, they seem destitute of any 



309 "I N A U 



powerful means of prehension and 

 detention. The eye, also, is reduced 

 to the simplest condition that the 

 organ of vision can assume, without 

 departing altogether from the type 

 of the higher classes, so that it 

 appears not far removed from that 

 of the proper molluscs. The nau- 

 tilus has only a single heart, the 

 branchial one being absent. The 

 nautilus resides in the capacious 

 cavity of its first, or external, 

 chamber ; and it is now well ascer- 

 tained that this animal is not a 

 piratical parasite, occupying the 

 shell of another animal, which it 

 has murdered, but that it lives, and 

 sails, in a skiff of its own building. 

 A siphuncle connects the body of 

 the nautilus with the air chambers, 

 passing through an aperture and 

 short projecting tube in each trans- 

 verse septum, till it terminates in 

 the smallest chamber at the inner 

 extremity of the shell. These in- 

 ternal chambers contain only air, 

 and have no commnnication with 

 the outer chamber but by one small 

 aperture in each septum through 

 which the siphuncle passes. No 

 water can by any possibility pass 

 into these chambers, between the 

 exterior of the siphuncle and the 

 siphonic apertures of the transverse 

 plates, because the entire circum- 

 ference of the mantle in which 

 the siphuncle originates, is firmly 

 attached to the shell by a horny 

 girdle, impenetrable by any fluid. 

 The number of chambers varies 

 greatly, according to the age of the 

 animal. Dr. Hook states that he 

 has found in some shells as many as 

 forty. The siphuncle, as appears from 

 Prof. Owen's statement, terminates 

 in a large sac surrounding the heart 

 of the animal; if we suppose this 

 sac to contain a pericardial fluid, 

 the place of which is alternately 

 changed from the pericardium to 

 the siphuncle, we shall find in these 

 organs an hydraulic apparatus for 



