648 TEXT-BOOK OF ENTOMOLOGY 



are such as occur in an insect which is enormously voracious as a 

 larva, and which often, passing through a period of complete in- 

 activity, taking no food at all, finally becomes an insect which needs 

 to suck in only a minimum quantity of water or nectar, and which 

 practically abstains from all food. The head and genital glands 

 also, as well as the urinary vessels, are nearly the same. On the 

 other hand, the salivary glands have undergone, in the imago, a 

 thoroughgoing reduction. 



The changes undergone by the nervous system of Sphinx ligustri 

 and Vanessa urticce, have been described by Newport with fulness of 

 detail. An abstract of his observations on Vanessa urticce, which 

 undergoes its changes in June in 14 days, and in August in eight 

 days, we will now give, in part verbatim, the subject being rendered 

 much clearer by his figures, which are reproduced. 



During the last larval stage, certain changes have already taken place in dif- 

 ferent parts of the cord, which shows that they had been a long time in progress. 

 Besides the lateral approximation of the cords, the first change consists in a 

 union of the llth and 12th ganglia, the latter one being carried forwards ; these 

 two ganglia being entirely separate before the 3d moult. 



Two hours after the larva of Vanessa urticce has suspended itself in order to 

 pupate, the brain is not yet enlarged, but the subcesophageal ganglion is nearly 

 twice its original size and the ganglia behind are nearer together. "A little 

 while before the old larval skin is thrown off there is great excitement through- 

 out the body of the insect." About half an hour (Fig. 603,2) before this oc- 

 curs the alary nerves and the cerebral, 2d, 3d, 4th, and 5th ganglia are slightly 

 enlarged, and the 1st suboesophageal ganglion very considerably. Immediately 

 after the insect has entered the pupa state (Fig. 603, 3), all the ganglia are 

 brought closer together. One hour after (Fig. 603, 4) pupation the cerebral uan- 

 glia are found to be more closely united, the 4th and 5th ganglia are nearer, and 

 the distance between the remaining ganglia is also reduced. 



Seven hours after pupation there is a greater enlargement of the cerebral gan- 

 glia, optic nerves, and ganglia and cords of the future thoracic segments. 



At 12 hours (Fig. 603, 5) the 5th pair of ganglia has almost completely coa- 

 lesced with the cord and the 4th; at 18 hours (Fig. 603, 6) the whole of the ganglia, 

 cords, and nerves have become more enlarged, especially those of the wings, 

 while the 4th and 5th ganglia of the cords have now so completely united as to 

 appear like an irregular elongated mass. At 24 hours (Fig. 604, 7) the 4th and 5th 

 ganglia are completely united, the 5th being larger than the 4th. At 06 hours 

 (Fig. 604, s) the optic nerves have attained a size almost ecmal to that of the 

 brain. The 1st subcesophageal ganglion now forms, with the cerebral ones, a 

 complete ring around the oesophagus, the crura having almost disappeared. 

 The (5th ganglion has now disappeared, but the nerves arising from it remain. 

 At 48 hours ( Fig. 604, 9) the cord is straight instead of being sinuous, and the 

 7th ganglion has disappeared, while the thoracic ganglia are greatly enlarged. 

 At. the end of 58 hours the 2d and 3d thoracic ganglia have united, and the 

 double ganglion thus formed is only separated from the large thoracic mass com- 

 posed of the 4th, 5th, and part of the 6th ganglia, by the short but greatly en- 

 larged cords which pass on each side of the central attachment of the muscles. 



