CENTRALIZATION OF THE NEKVOUS SYSTEM. 



361 



ments in comparison with those of the mature imago. The senses ex- 

 hibit equal imperfection ; and eyes are either entirely wanting, or are 

 mere ocelli simple specks, exhibiting the lowest possible organization 

 of a visual apparatus. But as the growth of the larva goes on, a change 

 in the arrangement of the nervous system is perpetually in progress. 

 The series of nervous cords connecting the different pairs of ventral 

 ganglia in the larva (fig. 182, A) become flexuous as the insect attains 

 the pupa state ; the whole chain becomes shorter ; the brain, or ence- 

 phalic ganglion, increases in its proportionate dimensions ; and, more- 

 over, several ganglia, originally distinct, coalesce, and form larger and 

 more powerful masses (fig. 182, B). This coalescence of the ganglia, 



Changes which the nervous system undergoes during the progress of Insect metamorphosis. 

 A, Nervous system of the Larva. B, that of the Pupa. C, that of the Imago or perfect insect. 



which takes place more especially in the thoracic region, is evidently 

 a preparation for the concentration of greater power and activity in this 

 part of the body ; and although in inactive chrysalides this change is 

 not as yet visible by its effects, in the active forms even the pupa is 



