CHARACTERISTICS OF CUTTLEFISHES. 331 



In the head the cerebral, pleural, and pedal pairs of 

 ganglia are concentrated around the gullet, and protected by 

 a cartilaginous box, analogous after a fashion to the Verte- 

 brate skull. As we would expect in active adventurous 

 animals, eyes and other sensitive structures are generally well- 

 developed. 



The mouth is armed with hard jaws like a parrot's beak, 

 and there is the usual rasping tongue or odontophore. 



Two pairs of gills in Nautilus, one pair only in the others lie 

 posteriorly in the mantle cavity, and it is there that the food- 

 canal, the kidney ducts, and the genital duct all end. 



The vascular system is very well developed, the heart with 

 two auricles and a ventricle lies in an unusually large peri- 

 cardial chamber. The kidneys are large and saccular. 



The sexes are separate. The male elements are made up 

 in packets or spermatophores, which are usually transferred 

 to one of the " arms," more or less modified for copulatory 

 purposes. The eggs are large, and often surrounded by 

 capsules. 



Considering the large quantity of yolk in the egg, we 

 do not wonder that the development differs much from 

 that of bivalves and Gasteropods ; the trochosphere and 

 veliger stages are not recognisable as such. 



There are at least two sets — (i) the Nautiloids, of which 

 the Pearly Nautilus is the only living representative, and 

 along with which the extinct Ammonites are usually asso- 

 ciated ; (2) the Octopod and Decapod cuttlefishes, along 

 with which the extinct Belemnites are included. 



A Type of Cuttlefish — Sepia officinalis. 



Mode of Life. — This common cuttlefish is widely distri- 

 buted, especially in warmer seas like the Mediterranean. 

 Unlike the Octopus, which usually lurks passively, Sepia 

 swims actively, gently moving the fins which fringe the 

 body, or jerking itself energetically backwards by the out- 

 gush of water through the funnel. It likes the light, and is 

 sometimes attracted by lanterns. The beautiful colours 

 change according to external conditions and internal emo- 

 tions; and a plentiful discharge of ink often covers its 



