182 CLASSIFICATION OF THE ANIMAL KINGDOM. 



a portion of the vast surface of the globe, yet the animals belonging to 

 this class possess a nervous system which fully entitles them to be placed 

 in the high position they hold as regards the general Animal Kingdom, 

 and is, in fact, necessarily commensurate with the superior development of 

 their various organs. The nerves are easily discoverable, as they are of a 

 pale red colour; and the ganglia, instead of being found in scattered masses 

 dispersed through the body, according to the usual Heterogangliate type, 

 are concentrated in the form of a ring round the oesophagus. There are 

 eight large and two smaller masses in this part, and from them are given 

 off filamentary nerves to all parts of the body, a type of structure which 

 would seem to bear the same relation to the former classes of this division 

 as that of the Spiders does to the lower orders of the Homogangliate 

 world. The different genera resemble one another in most of the important 

 types of their structure, with only a few modifications. Some species possess 

 thin glassy shelly plates on the dorsal and ventral aspects of their bodies, 

 and others have small spiral shells. Tn our own immediate seas this class 

 is not numerous, and we possess only a few species. 



Tn the last class of this division, the Cephalopods, we find animals of 

 a very peculiar description, and presenting a much higher state of develop- 

 ment than anything we have hitherto met with. They are divided into 

 two great orders, the Dibranchiate and Tetrabranchiate Cephalopods, from 

 the number of their respiratory organs.- The former are the most numerous, 

 comprising all the animals of this class now in existence, except the Nautilus 

 Pompilius. The body of the Cephalopods consists of a bag, enclosing the 

 viscera and organs of digestion, and a head furnished with a pair of eyes 

 and a number of singular tentacula armed with powerful suckers, which 

 vary considerably both in shape and size in different species. The eyes 

 are generally large and staring, but their structure in the two divisions 

 differs materially; those of the Tetrabranchiate Nautilus are very simple, 

 and are attached to the head by pedicles, while those of the Dibranchiate 

 order are much superior, and conform somewhat in type to the visual 

 organs of vertebrate animals. The mouth in all Cephalopods is placed near 

 the centre of the feet-like tentacula, and is generally surrounded by a thick 

 circular lip, which encloses a pair of horny jaws or mandibles, resembling 

 a parrot's beak turned upwards. Inside this beak is a fleshy lobed tongue, 

 partly covered with sharp recurved hooks, as in Pteropoda. The oesophagus 

 is short, leading quickly into a large dilating crop, which is succeeded by 

 a powerful muscular gizzard, passing into a simple slightly convoluted 

 intestine, and which, analogous to that of the Pteropods, mounts up to the 

 head, at the base of which the anal aperture is situated. The liver is of 

 a large size, and the bile is poured into a singular chamber appended to 

 the head of the intestine, with which it communicates. Besides the organs 



