9O Invertcbrata. 



CHAPTER XVII. 



CUTTLEFISHES. 



CLASS IV. Cephalopoda. The highest class of mol- 

 luscs is that which consists of Nautili, Cuttlefishes and 

 Squids. These are all highly organised marine animals 

 with a central mouth, around which there are processes 

 of the foot, disposed in the form of a circlet of arms 

 or tentacles ; each of these arms is provided with one 

 or more rows of large suckers, and thus they form a 

 powerful grasping organ, which they use in taking the 

 prey whereupon they feed. 



Shells. Very few of these are enveloped in shells, 

 and most of them progress, when creeping, with the 

 head down, and with the large mantle cavity at the 

 hinder side. There are three kinds of shells found 

 clothing, or contained in, some animals of this class. 

 These are ist. The chambered shell, such as that of 

 the pearly nautilus (fig. 54, p. 92), a coiled spiral 

 divided by numerous partitions into successive cham- 

 bers (/;), each of which, however, communicates with 

 the neighbouring chambers by means of a tube or 

 siphuncle (c). 2. The enclosed shell, a horny or calca- 

 reous plate or oval mass, embedded in the integu- 

 ment, or lying in a closed cavity along the front 

 wall of the animal's body ; such a shell is found in 

 the cuttlefish and squid. 3. In one species there 

 is a singular shell secreted by two of the arms 

 which lie beside the mouth, and which are flattened 

 organs, and the shell so secreted is a slightly spiral 



