THE VICTORIAN NATURALIST. 31 



in a curious manner, being at first enveloped in a kind of cyst, 

 which later on bursts and allows the arm to expand to its full 

 extent, when it greatly exceeds in length the other arms. It is 

 furnished with suckers for part of its length, the remainder con- 

 sisting of a long thread-like organ. This is known as the hecto- 

 cotylus arm. The male has the power cf detaching this arm, 

 which it leaves within the mantle-chamber of the female, and 

 which retains the power of independent movement for some con- 

 siderable time. It was owing to one of these being discovered 

 within the mantle of the female which led to its being described 

 by Cuvier as a parasite, under the name of Hectocotylus 

 octopodis. 



The Argonaut is readily distinguished from the Nautilus, owing 

 to the latter being permanently attached to its shell, the arms 

 being numerous, short and pointed, and devoid of suckers, and 

 the absence of an ink-bag. The shell is divided into a number 

 of chambers by regularly curved divisions or septa. These septa 

 are perforated in the centre to allow of the passage of a long, 

 narrow tube known as the siphuncle, the use of which is un-. 

 known, which traverses the whole length of the shell to the apex, 

 and is connected with the animal, which occupies the outer 

 chamber. The Pearly Nautilus belongs to the order Tetra- 

 branchiata, and is the only living Cephalopod which is provided 

 with four gills. It is the sole surviver of the order, and includes 

 among its fossil relatives the beautiful and well-known 

 Ammonites. The genus embraces four living species, three of 

 which have been recorded from the New South Wales and 

 Queensland coasts, but none have been known so far to occur in 

 Victorian waters. Shells of all these species are represented in the 

 National Museum collection, two of which contain the animal. 



There are many points in the history of this animal which 

 still require clearing up. Although shells containing the animal 

 and ova are very frequently collected, none, so far as I can 

 learn, have been found occupied by the newly-hatched young. 

 This would lead us to conclude that the young, which, 

 like other Cephalopods, grow very rapidly, desert the shell 

 of the parent immediately after hatching, and start out for 

 themselves. 



One of the questions which suggest themselves is, that as the 

 shell is regarded more as an egg-cradle than as a permanent 

 abode for the protection of the animal, does she either before or 

 shortly after the hatching of the ova purposely desert her shell ; 

 and if such be the case, does she then die ? Sir F. M'Coy, in the 

 "Prodromusof Zoology of Victoria," vol. i., plate 6i, after describ- 

 ing the rapid variation of the colours of the animal, continues : — 

 " This colouring of the surface of the body, like naked Cuttle- 

 fishes, is another reason for believing that the shell is not a per- 



