THE CHAMBERED, OR PEARLY NAUTILUS. 311 



the Giant's Causeway in minature, as the irregular fracture breaks up their ranked columns 

 into deep caverns and bold projecting rocks. A diagonal cut with a knife will further expose 

 the hard horizontal strata, with their myriad pillars ; but the method by which the structure 

 exhibits itself in its greatest beauty is to make a very thin transverse section, mount it in 

 Canada balsam on a glass slide for the microscope, and employ polarized light in its 

 examination. 



In consequence of its peculiar formation, the cuttle-bone is extremely light when dry, and 

 admits so much air into the interstices that it swims easily in water. 



The eggs of the Sepia are dark oval bodies, looking something like a bunch of purple 

 grapes, and from this resemblance termed Sea Gfrapes by the fishermen. They may often be 

 found on the seashore, flung there by the retiring tide, and left to perish unless rescued by 

 some friendly hand. If these bunches of eggs be placed in a vessel of sea-water, and guarded 

 from danger, they may be seen daily changing in appearance, until at last they burst asunder 

 and let loose the inmates on the world. Nothing can exceed the nonchalant demeanor of the 

 tiny creature not two minutes old. It deliberately makes the tour of its glassy prison, 

 examines every detail with minute attention, and having quite satisfied its curiosity, poises 

 itself for a moment just above the ground, blows out a circular hollow in the sand with a sharp 

 expulsion of water from the siphon, and settles quietly into the bed thus prepared for it. 



The family Sepiadce embraces the true Cuttle-fishes. The genus Sepia furnishes the 

 well-known bone and ink of commerce. The flesh is esteemed in European sea-ports. The 

 family Loliginidce includes those forms known to us as Squids. Of the three living genera 

 only one — Loligo — is represented on our coast. L. pealei is the familiar form, seen on the Cape 

 Cod shores. It reaches a length of about fifteen inches. The species common north of Cape 

 Cod is Ommastr&phes illicebrosa. A second, L. brevis, extends from Virginia to Brazil. 

 L. galei inhabits the Gulf of Mexico. 



Before proceeding to another large group of cephalopods, it is needful to mention the 

 curious animals called, from the shape of their shell, Spiralidse. These singular creatures 

 form a distinct though very small family, containing only three species. 



In them, the shell is very delicate, and is rolled into a spiral form, something like the pro- 

 boscis of an elephant when curled up. These shells are very common on the shores of New 

 Zealand, where they are scattered in thousands, and are sometimes thrown on the shores of 

 Europe by the waves of the Gulf Stream. Yet the animal which formed the shell is extremely 

 rare, and is seldom found except in a very fragmentary and battered condition. 



TETRABRANCHIATA. 



Another order of cephalopods is called by the name of Tetrabranchiata, or Four-gilled 

 animals, because the organs of respiration are composed of four branchise. These creatures 

 possess a very strong external shell, which is divided into a series of gradually increasing com- 

 partments connected together by a central tube called the siphuncle. As the animal grows, it 

 continues to enlarge its home, so that its age can be inferred from the number of chambers 

 comprising its shell. 



In former times these creatures were very abundant, but in our day the only known living 

 representative is the Chambered, or Pearly Nautilus. The spiral home in which the 

 creature resides, and the structure of the chambers, together with their connection by means 

 of the siphuncle, is beautiful. 



While the animal still lives, the short tubes that pass through the walls of the chambers 

 are connected by membranous pipes, and even in a specimen that has been long dead, these 

 connecting links hold their places, provided that the shell has not been subjected to severe 

 shocks. In one of these shells now before me, which I have very cautiously opened, the 

 whole series of membranous tubes can be seen in their places, black and shrivelled externally, 

 but perfect tubes nevertheless. 



