10 ON CLASSIFICATION. 



1. Cirripeda. 4. Insecta. 



2. Annelida. 5. Araclmida. 



3. Myriapoda. 6. Crustacea. 



Fourth Division. HETEROGANGLIATA (Owen) ; Mollusca 

 (Cuvier)*; Cyclogangliata (Grant). 



(12.) The characters of this division are well defined, and the irre- 

 gular and unsymmetrical forms of the bodies of most of the genera 

 which compose it, in exact relation with the arrangement of the 

 nervous apparatus. 



As in the articulata there is a large nervous mass placed above 

 the oesophagus, which supplies the principal organs of sense, but 

 the other ganglia are variously dispersed through the body, although 

 always brought into communication with the supracesophageal 

 portion by connecting filaments. Throughout all the forms, we 

 find a distinct relation between the size and developement of the 

 nervous centres, and the perfection of the animal, indicated by the 

 senses and organs of motion with which it is provided. 



This division includes 



1. Tunicata. 4. Gasteropoda. 



2. Conchifera. 5. Pteropoda. 



3. Brachiopoda. 6. Cephalopoda. 



Fifth Division. VERTEBRATA (Cuvier); Myelencephala (Owen); 

 Spinicerebrata (Grant). 



(13.) The arrangement of the nervous centres in the highest or 

 vertebrate division, indicates the greatest possible concentration and 

 developement. The ganglionic masses assume a very great pro- 

 portionate size when compared with the nerves which emanate from 

 them, and are principally united into a long chain, denominated 

 the cerebro-spinal axis or cord, which is enclosed in a cartilaginous 

 or bony canal, occupying the dorsal region of the animal. The 

 anterior extremity of the cerebro-spinal axis is made up of those 

 ganglia which are more especially in relation with the principal senses 

 and the higher powers of intelligence, forming a mass denominated, 

 from its position in the skull which encloses it, the encephalon. 

 It is with the increased proportionate developement of this portion, 

 that the intelligence of the animal becomes augmented ; in the 

 lower tribes, the cerebral masses scarcely exceed in size those 



* The Cirripeda are included in the Mollusca of Cuvier. 



