286 



THE CEPHALOPODA 



body reduced (Fig. 22, E). This is the result of the displacement of 

 the foot, whose lateral borders surround the head and are joined 

 together in front of the mouth. In consequence of this shortening 

 of the antero-posterior axis, the two extremities of the digestive 



canal are closely approximated,- 

 cce and the pallial cavity opens im- 



mediately behind the head (Fig. 

 252, m, a). 



The head is highly developed, 

 but has hardly any other ap- 

 pendages than those formed by 

 the edges of the foot which 



an, 



FIG. 252. 



Diagram of the structure of a Cephalopod, 

 as seen from the left side in its proper mor- 

 phological position, a, anus ; ar, arms ; ce, 

 central nervous system, with eye ; coe, 

 coelom ; fu, funnel ; g, gill ; go, gouad ; h, 

 heart ; fc, kidney ; i, liver ; m, mouth ; 

 pa, mantle ; r.o, renal orifice ; r.p, reno- 

 pericardial orifice ; st, stomach. 



PIG. 253. 



Taonivs suhmii, Lankester, ventral 

 aspect, e, pedunculated eye ; ji, fin ; m, 

 mouth ; t, tentacular arm. (After Hoyla.) 



embrace it. Certain Oigopsida, however, e.g. Taonius suhmii, Bay 

 Lankester (Fig. 253), and the embryos of an allied form known 

 as Grenacher's embryo (Fig. 119, D) and of Loligo peali, have very 

 prominent pedunculated eyes. On the other hand, Nautilus, whose 

 eyes are also somewhat prominent, has in addition two ciliated 

 tentacles on either side of the head, one in front of and the other 

 behind the eye (Figs. 255, i, k; 293, a.o.t, p.o.t). 



The foot forms a crown of appendages surrounding the mouth : 

 the edges of this crown are not deeply divided in Nautilus, but 

 are much more so in the Dibranchia. In Nautilus the circumoral 

 pedal crown is divided into lobes each of which bears a group of 

 tentacles, the total number of tentacles being about ninety in the 



