ON CLASSIFICATION. 9 



and probably to the senses of taste and smell. This dorsal or 

 anterior pair of ganglia, which evidently is in relation with the 

 higher functions of the economy of the creature, is brought into 

 communication with the series of nervous centres placed along the 

 ventral aspect, by means of filaments which embrace the oesophagus, 

 and join the anterior pair placed beneath it ; the whole system 

 may therefore be regarded as a series of independent brains destined 

 to animate the segments of the body in which they are individually 

 placed. Such a multiplication of the central organs of the nervous 

 system, is obviously adapted to the elongated forms of the vermi- 

 form orders, but from the want of concentration which such an 

 arrangement implies, this type of structure is still very inferior in 

 its character. As the articulata become more perfect in their out- 

 ward form, the number of the brains becomes diminished, while 

 their proportionate size increases ; and thus in the carnivorous 

 Insects, Arachnida and Crustacea, they are all united into a few 

 great masses, which, becoming the general centres of the entire 

 system, admit of a perfection in their external senses, a precision 

 in their movements, and an energy of action, of which the detached 

 character of the ganglia in the lower tribes was incapable. 



(11.) This dependence of the perfection of the animal upon the 

 concentration of the central masses of the nervous system, is strik- 

 ingly proved by the changes perceptible in the number and arrange- 

 ment of the ganglia, during the progress of an insect through the 

 different stages of its existence. In the elongated body of the worm- 

 like caterpillar, each segment possesses its appropriate pair of ganglia, 

 and the consequence of such diffusion of its nervous apparatus, is 

 apparent in its imperfect limbs, its rude organs of sense, its sluggish 

 movements, and general apathy, but as it successively attains to 

 more mature forms of existence, passing through the different me- 

 tamorphoses which it undergoes, the nervous ganglia gradually 

 coalesce, increase in power, as they diminish in number, until in 

 the imago or perfect state, having arrived at the greatest concen- 

 tration compatible with the habits of the insect, we find it endued 

 with new and far more exalted attributes, the organs of its senses 

 are more elaborately formed, it possesses limbs which previously it 

 would have been utterly incapable of wielding, its movements are 

 characterized by their activity and precision, and its instincts and 

 capabilities proportionately enlarged and exalted. 



The Homogangliate division of the animal world is extremely 

 natural, and includes the following classes : 



