ORGANIC DEVELOPEMENT. 605 



in pairs and in a longitudinal series, like those 

 we have seen constituting the permanent form 

 of the brain in the inferior fishes : but, in birds, 

 they are soon folded together into a rounded 

 mass ; while, in the mean time, the two filaments 

 of the spinal cord have approached each other, 

 and united into a single column, the form which 

 they ever after retain. Even at this early period 

 the rudiments of the organs of the higher senses, 

 (first of the eye, and next of the labyrinth of the 

 ear,) make their appearance : but, on the other 

 hand, those of the legs and wings do not show 

 themselves until the brain has acquired greater 

 solidity and developement. The nerves which 

 are to connect these organs of sensation and of 

 motion with the spinal cord and brain are formed 

 afterwards, and are successively united to tlie 

 nervous centres. 



Although the plan of the future edifice has 

 thus been sketched, and its foundations laid in 

 the homogeneous jelly by the simpler efforts of 

 the vital powers, the elevation of the vast super- 

 structure demands the aid of other machinery, 

 fitted to collect and distribute the requisite 

 materials. Here, then, we might, perlia})s, 

 expect to meet with a repetition of those vege- 

 tative processes, having similar objects in view, 

 and the adoption of analogous means for their 

 accomplishment; but so widely different in cha- 

 racter is the whole organic economy of these two 



