CEPHALOPODA. 591 



is probable, however, that the ova derive an additional exterior co- 

 vering and connecting substance from the secretion of a large glan- 

 dular apparatus, which is situate immediately below the terminal 

 orifice of the oviduct. This apparatus is attached to the mantle, and 

 gives rise to the two rounded convexities observable on the ventral 

 aspect of the body behind the funnel. It is a transversely oblong 

 mass, composed of numerous close-set pectinated membranous la- 

 minae, which are about a quarter of an inch in depth, and are dis- 

 posed in three groups ; those of the larger group extend transversely 

 across the mesial line of the body, and are unprotected by a mem- 

 brane ; but the two smaller divisions are symmetrically disposed, and 

 have the unattached edges of the laminae covered by a thin membrane, 

 which is reflected over them from the anterior margin of the glandular 

 body. These divisions form the sides and anterior part of the gland ; 

 and as the secreted matter must pass backwards to escape from be- 

 neath the margin of the protecting membrane, this membrane may 

 serve both to conduct the secretion nearer the orifice of the oviduct, 

 and also to prevent its being drawn within the respiratory currents of 

 water, and so washed away as soon as formed. 



In contrasting the organisation of the Nautilus with that of the in- 

 ferior Mollusca treated of in the two preceding Lectures, we find the 

 main advance to have been made in the organs of animal life. 



A true internal skeleton is established in the Nautilus, and thus the 

 lowest Cephalopod offers an approximation to the Vertebrate type, 

 which not even the highest of the Articulate series had attained. 

 Perfect symmetry now reigns throughout the animal and vital organs. 

 The muscular system forms a larger proportion of the body, with va- 

 rious arrangements and complications unknown in the lower Ence- 

 phalous moUusks. The respiratory tube, though still completed by 

 the overlapping, not by the coalescence, of its side-walls, has re- 

 ceived an enormous development as contrasted with the siphonated 

 Trachelipods ; and, by its powerful muscles and their firm cartila- 

 ginous basis of attachment, it is evidently endowed with a new func- 

 tion, in relation to propelling the Cephalopod with its testaceous 

 dwelling through the sea. 



The nervous centres concentrated in the head have received a 

 marked increase of bulk, which, nevertheless, is still manifested more 

 strongly in the inferior masses, and especially the anterior suboeso- 

 phageal ring than in the superior or cerebral part. Here, however, 

 we find for the first time in the Molluscous series, especial ganglions 

 subordinated to the greatly enlarged organs of vision. 



The organs of reptation, which had progressively advanced (as 

 Lamarck's denomination of the higher Gastropods indicates) towards 



