9 



The mention of Cephalopoda with an internal support implies also 

 the existence of Cephalopoda with an external shield. The type of 

 this last group is met with in the Pearly Nautilus, 1 whose beautiful 

 outline and splendid lustre, are known to all. 



Professor Owen, in a memoir 2 written on the subject, has very fully 

 pictured and described the being which 

 owns the Nautilus-shell as its house 

 and home, and has shown the wonder- 

 ful adaptation of parts and means to an 

 end, which in that, as in every other 

 case of Nature's works, strikes a 

 thoughtful beholder. Not the least 

 curious characteristic in reference to 

 the Nautilus animal, is its shell (fig. 3), 

 a castle capable of excluding doubtful 

 spies, the floors for strengthening the 

 castle walls, the machinery for repair- 

 ing damages, and lastly, the absence of 

 an ink-bag, and the existence of a less 

 vigorous frame, two things not required, when there is a house for 

 habitation, and a door which can be locked. 



For a moment let us investigate the shelly covering alone, and 

 note its most conspicuous parts. Externally we find a case (fig. 3) 

 of thin calcareous substance, elegantly designed in agreement with 

 that curve called an involute or flat spiral, the case itself having 

 slightly compressed sides, a rounded back, and an opening of some 

 size. On our cutting a transverse section of this case, marvellous 

 seems the arrangement of the internal parts, the whole being divided 

 into rooms by pearly walls and floors, each room after the outer and 



1 Aristotle, in his History of Animals, Lib. iv., cap. 1, gives us the name, and very 

 clearly describes the nature of the Paper and the Pearly Nautilus in the following 

 terms. " There are also two other genera of polypi which are in shells, one of which 

 is called by some Nautilus and by others Nauticus. This genus resembles a polypus 

 (iro\vTrovs), and the shell is similar to a hollow pecten (ktzis), but is not perfectly 

 affixed to it (ffvfxcpvris). . . . there is also another polypus, which is covered with 

 a shell like a snail, so that it never leaves its shell, but sometimes outwardly extends 

 its arms." 



' * On the Pearly Nautilus. London, 1832. 



Fig. 3. 



Nautilus pompilius, (Pearly Nautilus) 

 drawn from a specimen in the College 

 of Surgeons. A portion of the shell has 

 been removed to show the siphuncle 

 and empty chambers, part of the valve- 

 like mantle and the brachial tentacles 

 of the animal are seen projecting from 

 the mouth of the shell. These tentacles 

 correspond to those of the Loligo, 

 but are more numerous and without 

 suckers; the mantle acts as an oper- 

 culum. 



