270 



to its own division alone ; at least to have very little dependence upon the 

 other segments of the Animal. In short, to borrow an allusion from our local 

 politics, these creatures may be said to have ultra-provincial constitutions. 



Next we come to the Two Sub-Kingdoms, immediately beneath the Yer- 

 tebrata ; and these indeed present a sharp and interesting contrast. On the 

 one hand the Mollusca represent the gradually increasing perfection of the 

 apparatus for the discharge of the functions of Organic, or Vegetative Life — 

 creatures, for the most part, sluggish and inert, yet greedy and voracious ; 

 " whose God is their belly " ; as Carpenter quaintly remarks of them. On the 

 other hand the Articulata are generally characterised by the rapidity of their 

 movements, the great, and sometimes enormous, proportionate strength of their 

 muscles, the extraordinary instincts displayed by some members of the group, 

 and the large endowment of nervous force with which these various gifts are 

 connected, and on which they are, in a physical sense, dependent. Thus the 

 Articulata represent the gradually increasing perfection of the Nervous or 

 Animal Life. 



In the Mollusca the Nervous System is by no means so striking a feature 

 of the organisation. In many of the lower members of the class the mouth is 

 the only indication of a head ; the organs of sight, if they exist, are imperfectly 

 evolved. But in the higher classes the case is different. Many of these 

 possess the senses of sight and hearing, and the organs of these senses are 

 collected ^^pon a Head, about which the Nervous ganglions are concentrated. 

 But even in the highest class of Molluscs the Nervous System appears sub- 

 servient to the sensorial and nutritive functions. 



Turning to the Articulata, we find very distinct indications of an approach 

 in Nervous structure to the Vertebrata. The characteristic feature is a double 

 Nervous cord studded with ganglia at intervals, there being one ganglionic 

 centre for each segment (or division) of the Animal. The more alike the 

 diffei'ent segments, the more equal are the ganglia. In the lower classes, all 

 the segments of the trunk being nearly of a size, so are the ganglia ; and the 

 power of each ganglion is almost wholly confined to its own segment. In this 

 they resemble the Radiata ; the chief difference being that the segments of the 

 latter are disposed in a radiate manner, whilst in all the Articulata they are 

 longitudinally arranged. But in the higher Articulata, the great power of the 

 Nervous System is concentrated about the head and thorax (chest). The 

 ganglia of the head are always larger and more impoi^tant. They are connected 

 with the organs of Sight and other Special Senses, and evidently possess a 

 power of directing and controlling the movements of the entire body, whilst 

 the power of each ganglion of the trunk is, as already said, mostly confined to 

 its own segment. It is obvious that the double Nervous Cord of the Articu- 

 lata corresponds with, and as it were pre-figures, the Spinal Cord of 

 Vertebrata ; and that the cephalic ganglia (ganglia of the head) correspond 

 with the contents, at least with a portion of the contents, of the Vertebrate 

 skull. 



In the class of Insects which is the highest of the Sub-Kingdom 

 "Articulata," the development of pure instinct reaches its highest point. Ants 

 and Bees are equalled by no other creature in the geometrical precision of their 

 structures, their perfect adaptation of means to ends, and the absolute regu- 

 larity with which each member of their wonderful societies performs its allotted 

 part in the economy of the nest or hive. And as pure instinct culminates in 

 these creatures, it would seem that the higher Articulata should be treated as a 

 lateral branch of that great tree of Organic Life, of which we have been as it 

 were, tracing the upward growth. In their own line, there is nothing superior 

 or equal to the Social Insects. 



Another observation tends in the same direction, it is this : as regards all 



