INSECTA. 303 



patient investigation, succeeded in detecting the undeveloped ru- 

 diments of the future sexual organs both of the male and female. 

 It is during the maturation of the pupa that these important parts 

 expand ; and, before the disclosure of the imago, they are found to 

 have attained their complete proportions, so as to be ready to per- 

 form their functions as soon as the expansion of the wings endows 

 the insect with means of locomotion sufficiently perfect to ensure 

 the due dispersion of the species. 



(349.) It is in the nervous system, however, that the most in- 

 teresting phenomena are observable ; and in the lessons afforded by 

 watching the correspondence between the state of the animal during 

 the several phases of its existence and the developement of the ner- 

 vous ganglia, the physiologist cannot fail to recognise those great 

 and general principles upon which our arrangement of the animal 

 creation is based. In the worm-like larva the ganglia are numerous 

 but of small dimensions ; too feeble to be capable of animating 

 powerful limbs, or of appreciating impressions from the organs of 

 the higher senses : the animal is, in fact, precisely in the condition 

 of an ANNELID AN, which it would seem to represent. External 

 limbs are therefore absolutely wanting in many larvae ; in others 

 they are represented by short and stunted appendages ; and even in 

 the most perfect, or hexapod larvae, they are feeble instruments in 

 comparison with those of the mature imago. The senses exhibit 

 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 (Jig. 138, A) become flexuous as the 

 insect attains the pupa state ; the whole chain becomes shorter ; the 

 brain, or encephalic ganglion, increases in its proportionate dimen- 

 sions ; and, moreover, several ganglia, originally distinct, coalesce, 

 and form larger and more powerful masses (Jig. 138, B). This co- 

 alescence of the ganglia, 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 distinguished from the larva 

 by a considerable increase of vigour and energy in its movements. 

 In the imago the concentration of the nervous centres is carried to 

 that extent which is adapted to the necessities of the mature state ; 



