296 PTILOTA : INTERNAL ANATOMY. 



stages of its passage to perfection, with the perfect state 

 of the inferior animals. 



In the larva there are thirteen knots, corresponding with 

 the number of rings of the body ; but these organs, like the 

 other internal systems, are modified during the passage to 

 the perfect state. Thus Dr. Herold, in his celebrated work 

 upon the Internal Anatomy of the White Garden Butterfly, 

 ascertained, as the larva approached matm-ity, that the second 

 ganglion became united with the first ; the fifth and sixth 

 approach and unite, then the third and fourth, whilst in the 

 pupa the seventh and eighth have entirely disappeared ; so 

 that, instead of thirteen, the imago possesses but eight 

 ganglia. 



On examining the invertebrated, or rather the externally 

 vertebrated structure of an insect with that of the internally 

 vertebrated animals, we find no part corresponding with the 

 brain; or rather the organ which in the former might be re- 

 garded as analogous thereto, and which, indeed, has been 

 called the brain, namely, the ganglia of the head, is repeatedly 

 represented along the entire length of the body : consequently 

 it has been supposed that the nervous cord of the insect re- 

 presents the great sympathetic nerve of the latter, although, 

 perhaps, it would be more correct to regard it rather as the 

 spinal cord. 



The matter of which the nerves are composed is a soft 

 pulpy substance, inclosed in a simj^le and transparent mem- 

 brane. 



The first pair of ganglia is always situated in the head of 

 insects, above the digestive canal, and is furnished with 

 nerves extending to the eyes, antenna, mandibles, maxillae, 

 and labrum. The other gangUa are lodged in the thorax 

 and abdomen, or in the former alone, and similarly placed 

 above the alimentary canal ; the two thick nervous filaments 

 connecting the head ganglia with the prothoracic gangHa are 



