766 



ZOOLOGY 



SECT. 



penis (Fig. 689, pen.). In the female the right oviduct has a 

 glandular dilatation, which is supposed to be an albumen gland. 

 The ova are of large size, greatly exceeding those of Sepia in 

 dimensions, containing a large proportion of food-yolk. Nidamental 

 glands are present, but are mainly situated, as already pointed 

 out, on the posterior instead of the anterior wall of the mantle- 

 cavity. Each egg becomes enclosed in an elaborate capsule (Fig. 

 695), probably moulded by the agency of the organ of Owen, on 

 the inner posterior lobe of the foot of the female (Fig. 686). The 

 development is not known. 



r.t?e-n.op 



FIG. 694. Nautilus pompilius, female reproductive 

 organs, alb. albumen-gland ; I. gen. op. left genital 

 opening ; oy. ovary ; pyr. pyriform appendage ; r. gen. 

 op. right genital opening ; vent, ventricle. (After 

 Lankester and Bourne.) 



FIG. 695. Egg of Nautilus 

 macromphalus, enclosed 

 in its capsule. (After Willey.) 



2. DISTINCTIVE CHARACTERS AND CLASSIFICATION. 



The Cephalopoda are bilaterally symmetrical Mollusca, which 

 have the main part of the foot displaced forwards to the neigh- 

 bourhood of the mouth and divided into a series of arms bearing 

 suckers, or of lobes bearing tentacles, while the remainder of the 

 foot forms a funnel for the egress of water from the mantle-cavity. 

 The visceral mass is symmetrical and not coiled. The mantle 

 encloses posteriorly and ventrally a large mantle-cavity, in which 

 are situated the ctenidia and the renal, reproductive, and anal 

 apertures. The shell may be absent or rudimentary ; when present 

 and well developed, it may be internal or external, undivided, 

 or divided internally by septa into a series of chambers. There is 

 an internal cartilaginous skeleton, supporting and protecting the 

 nerve-centres and giving attachment to muscles. The mouth is 

 provided with a pair of horny jaws, and an odontophore is present. 



