THE METAMORPHOSES OF THE NERVOUS SYSTEM. 



43 



in the active larva. A little while before the old skin is thrown 

 off there is great excitement throughout the body of the insect. 

 About half an hour before this occurs there is a considerable 

 enlargement of the brain, the sub-oesophageal, and the second, 

 third, fourth, and fifth ganglions. The cords that extend between 



METAMORPHOSIS OF THE NERVOUS SYSTEM OF Vanessa tirtica. 



5. Twelve hours after changing. 6. Eighteen hours after changing. 7. Twenty-four 

 hours after changing. 8. Thirty-six hours after changing. (After Newport.) 



them diverge very much, and those between the fifth, sixth, and 

 seventh ganglions are disposed in a zig-zag direction. 



" Immediately after the insect has entered the pupa state all 

 the ganglions are brought closer together, in consequence of the 

 cords being disposed more irregularly than at any other period, 

 which has been occasioned by the shortening that has taken 

 place in every segment, by which the cords are rendered too 

 long to lie in a direct line. Seven hours afterwards there is a 

 greater enlargement of the brain, optic nerves, and ganglions 

 of the thoracic segments, which begin to approach each other. 



