124 Mr. Lovell Reeve on the Pearly Nautilus. 



trivance the volume and comparative buoyancy of its shell to 

 . keep pace with the surrounding pressure, which naturally in- 

 creases in intenseness as the subject increases in bulk ; the 

 other having a different medium to combat with, namely, the 

 outward increase of the coral in which it is imbedded, leaves 

 its spiral plan of construction to pursue a straight growth, 

 and, raising itself forward, fills the vacated portion of the shell 

 with an extraordinary secretion of solid matter. If the Ma- 

 gilus had advanced by a deposit of transverse septa, instead of 

 solidifying its shell, the increase of the madrepore might have 

 crushed it ; and if the Nautilus had advanced by the solidify- 

 ing of its shell instead of by the deposit of transverse septa, 

 it would have produced an incumbrance incompatible with its 

 locomotive faculties. 



We are now brought to the consideration of the habits of 

 the Nautilus. It is evidently, as Mr. Owen expresses it, " a 

 ground-dwelling animal," creeping along the bottom of the 

 sea, with hood and tentacles, at a tolerably quick pace ; and 

 the shell, being above its head, must greatly assist the animal 

 in its movements, from a tendency to float. It is not impro- 

 bable but that the Nautilus may use a certain hydrostatic in- 

 fluence over the branchial cavity to enable it to rise to the 

 surface. Valenciennes says, " It nage avec facilite dans te sein 

 des eausc enfaisant sortir avec force la grande quantite d'eau 

 contenue dans sa cavite branchiate" And the testimony of 

 Rumphius in respect to its capacity of floating, cited by Mr. 

 Owen, is of so much interest, considering the time in- which 

 it was written, that we venture to repeat it. 



u When he thus floats on the water, he puts out his head, 

 and all his barbs (tentacles), and spreads them upon the water 

 with the poop (of the shell) above ; but at the bottom he creeps 

 in the reverse position, with his boat above him, and with his 

 head and barbs upon the ground, making* a tolerably quick 

 progress. He keeps himself chiefly upon the ground, creep- 

 ing sometimes also into the nets of the fishermen ; but after a 

 storm, as the weather becomes calm, they are seen in troops 

 floating on the water, being driven up by the agitation of the 

 waves : whence one may infer that they congregate in troops 

 at the bottom. This sailing, however, is not of long continu- 

 ance ; for having taken in all their tentacles, they upset their 

 boat, and so return to the bottom." This account, published 

 at Amsterdam more than a hundred years ago, is mainly au- 

 thenticated ; but it may still be a little exaggerated, for the 



* By force of gravity probably. 



