182 NATURAL HISTORY. 



Rumphius's statement is peculiar to Spirula among Cephalopoda ; nevertheless it does, no doubt,, 

 occasionally float at or near the surface, and swim, after the manner of its kind, by the ejection of 

 water through the funnel from its branchial sac. The animal has also a minute ink-bag, by which, if 

 needful, to conceal its retreat by clouding the water, as in others of its class. 



Spirula has the same number of arms (eight) and of tentacles (two) as in other Decapodout; 

 Cuttles. The arms are short and provided with minute irregularly-scattered acetabula, or suckers. 

 The beaks are horny and well developed for the size of the animal. 



The shell itself offers important points of difference from the other living members of its order, 

 and at the same time connects it in a remarkable manner with the extinct group, the Belemnitidm, 

 on the one hand, and with the Pearly Nautilus and the Tetrabranchiata, or four-gilled division, on 

 the other. If we compare its shell with that of the Argonaut, which is the only other convoluted 

 internal shell in its own division, we see that the latter has no chambered portion, that it is only a- 

 simple " nidamental shell," developed in the female as a receptacle for the ova, and not in any way 

 organically connected with the animal. In Spii'ula it is a complex structure, divided up into 

 chambers, and these each peneti'ated by a delicate pearly tube, called a "siphuncle." The shell is, 

 moreover, organically united to the animal, serving as the point tfajypni of the retractor muscles of 

 the funnel and of the head, with its locomotive and prehensile organs. 



The shell is, moreover, sinistral (or left-handed), so that its relation to the soft parts of the 

 animal is exactly the reverse of that of Nautilus. Left-handed shells in the Snail and other 

 Gasteropoda are not uncommon, as we shall see presently. 



Dr. S. P. Woodward mentions that he had formerly in his cabinet an Argonaut shell with the 

 nucleus reversed, implying that the animal had turned right round in its shell, and then had continued 

 to add to it in the opposite direction. This would be impossible for any mollusc whose shell was. 

 organically attached to the body of the animal. 



D'Orbigny has described, under the name Spirulirostra, an elegant little fossil shell from the 

 Miocene Tertiary beds of Turin, in which the upper part consists of a chambered portion (or 

 " phragmacone ") with a siphuncle, coiled into a spiral, the volutions of which are 

 separated. This Spirula-like shell is lodged in a pointed calcai-eous portion, or rostrum, 

 corresponding to the guard of the Belemnite. This interesting fossil thus serves as a 

 link between the living Spirula and the fossil Belemnites ; for if a guard were added 

 to the shell of Spirula it would be converted into a form like a Spirulirostra. 



It seemed as if this little Cephalopod were destined to remain long a great rai'ity, 

 although so abundant in its ordinary habitat. The late lamented M. Pourtales 

 informed the writer that he was present in 1879 in the Museum of the Jar-din 

 des Plantes, Paris, when a sea-captain offered ten specimens of the shells of 

 Spirula to the Museum. Being told they were very common, and that it was 

 the animal which was the rarity desired, he replied that he had taken all these 

 ten examples alive in the open sea, with the animal, and had with his own 

 hands cleaned them and removed the animal matter, being ignorant of their value ! 

 Doubtless [like the elegant EupJectetta aspergillum, a single specimen of which was 

 originally sold to the British Museum for 30, and which, when Mi\ Moseley visited 

 Abu, in the Philippines (1875), "were a 'drug' in the market, and were brought off 

 Woodward] ^ ^ ie sn ^P ^ n washing-baskets full, and sold at two shillings a dozen "] these rare 

 little Cephalopoda will be met with alive in numbers, and we shall know their complete 

 natural history from fresh and perfect specimens ; they may even be watched in our Aquaria in 

 the living state, as they probably were by the old Dutch naturalist, Rumphius, in 1 704. 



The ten-armed section of the Dibranchiate Cephalopoda approaches most nearly to the Tetra- 

 branchiate division, not only in the fact of their more numerous feet, and the frequent development of an 

 internal circular series of eight short labial tentacles, but also by several internal characters: as, for 

 example, the single oviduct and detached glands for secreting nul amentum* ; the valve of the funnel; 



* The material with which the eggs of the mollusca are cemented together, or enveloped, and which is secreted by the 

 nidamental (or " nest-forming ") gland ffrom the Latin nidus, a nest). This organ is largely developed in the female of all 

 the Gasteropods and f'ephalopods. 



