INTERNAL ANATOMY OF INSECTS. 25 
last ganglions have nearly disappeared, and the chords 
of the three first internodes have again approached each 
other*, The next change exhibited is the absorption of 
the first ganglion by the brain, the union of the chords 
of the first internode, which is now straight, the approxi- 
mation of the second and third ganglions, and the en- 
largement of the one formed by the union of the fourth 
and fifth, at the expense perhaps of the sixth and seventh, 
which have now entirely disappeared, and in their place 
is a very long internode. These united ganglions retain 
the pairs of nerves they had when separate®. Just be- 
fore the assumption of the zmago, the direction of the 
lobes of the brain becomes horizontal, the second and 
third ganglions unite, and the internode between the 
third and fourth is shortened*. Lastly, when the animal 
is become a butterfly, the second and third ganglions 
have coalesced, and are joined to that formed by the union 
of the fourth and fifth; a short isthmus or rather constric- 
tion, with an orifice, being their only separation: each 
of these united ganglions send forth laterally four pairs 
of nerves*. In his figure, Dr. Herold has not repre- 
sented the orifice for the passage of the gullet, but doubt- 
less one exists, which for an animal that imbibes only 
fluid food is probably very minute. In Hypogymna dis- 
par, we learn from Cuvier, this orifice is of that descrip- 
tion, and of a triangular shape*. 
It can admit of no reasonable doubt that one of the 
principal intentions of these changes is to accommo- 
date the nervous system to the altered functions of the 
* Herold Schmeit. t. i. f. 7. b Prats XXX. Fic. 4. 
¢ Tbid. Fic. 5. -  ¢@ Thid. Fie. 6. 
* Anat. Comp. ii. 348. 
VOL. IV. 
