184 



CHAPTER XII. 



HOMOGANGLIATA (Owen). 

 ARTICULATA (Cuv.) ; ANNULOSA (Mac Leay). 



) The third great division of the animal kingdom includes 

 an immense number of living beings adapted by their conforma- 

 tion to exist under a far greater variety of circumstances than any 

 which we have hitherto had an opportunity of examining. The 

 feeble gelatinous bodies of the ACRITA are obviously only adapted 

 to an aquatic life ; and accordingly they are invariably found either 

 to inhabit the waters around us, or to be immersed in the juices of 

 living animals upon which they subsist. The NEMATONEURA, 

 likewise, are all of them too imperfect in their construction to ' 

 admit of their enjoying a terrestrial existence, for, possessing no 

 nervous centres adequate to give force and precision to their move- 

 ments, they are utterly incapable of possessing external limbs 

 endowed with sufficient power and activity to be efficient agents in 

 ensuring progression upon land ; neither are any of them furnished 

 with those organs of sense which would be indispensable for the 

 security of creatures exposed to those innumerable accidents to 

 which the inhabitants of a rarer element are perpetually obnoxious : 

 the NEMATONEURA therefore are, from their organization, neces- 

 sarily confined to a watery medium. 



But the type of structure met with in the HOMOGANGLIATA 

 admits of far higher attributes, and allows the enjoyment of a more 

 extended sphere of existence : senses become developed propor- 

 tionate to the increased perfection of the animal ; limbs are pro- 

 vided endowed with strength and energy commensurate with the 

 developement of the nervous ganglia which direct and control 

 their movements ; and instincts are manifested in relation with the 

 increased capabilities and more exalted powers of the various 

 classes as they gradually rise above each other in the scale of 

 animal developement. 



(228.) The most obvious, though not the most constant, cha- 

 racter which distinguishes the creatures we are now about to de- 

 scribe, is met with in their external conformation ; they are all of 

 them composed of a succession of rings formed by the skin or 



