84 BRITISH LEPIDOPTERA. 



tracheal linings are withdrawn from the spiracle as from the others 

 and as at each of the larval moults, but the cells that replace these 

 linings where the tracheae remain, now fail, and are, in fact, exhausted. 

 The pupa develops here no spiracle (but only a scar) nor any tracheal 

 tube from the spiracular position to the main trunk. It is of interest 

 to note that this 8th abdominal spiracle is the one that is of such 

 paramount importance in the dipterous larva, and that it equally 

 disappears on the change to pupa. 



The nervous system of the lepidopterous pupa is much nearer to 

 that of the imago than is that of the larva. Already the ganglia of 

 the central chain have (especially in the shortened thoracic areas) be- 

 come united, but the amount of centralisation, even then, is small 

 compared with the final imaginal nervous system. Packard gives 

 (Text-book of Entomology, p. 649) ten figures, after Newport, of the 

 changes in the nervous system of Aglaisurticae during and after pupation. 

 Packard (quoting Newport) writes : During the last larval stage certain 

 changes have already taken place in different parts of the cord, which 

 show that they have been a long time in progress. Besides the lateral 

 approximation of the cords, the first change consists in an union of the 

 11th and 12th ganglia, the latter one being carried forwards, these 

 two ganglia being entirely separate before the third moult. Two 

 hours after the larva of Aglais urticae has suspended itself for pupation 

 the brain has not enlarged, but the suboesophageal 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 throughout the body of the insect. About half-an-hour 

 before this occurs, the alary nerves and the cerebral, 2nd, 3rd, 4th, and 

 5th ganglia are slightly enlarged and the 1st suboesophageal ganglion 

 very considerably. Immediately after the insect has entered the pupal 

 state, all the ganglia are brought closer together. One hour after 

 pupation the cerebral ganglia are found to be more closely united, the 

 4th and 5th ganglia are nearer, and the distance between the remain- 

 ing ganglia is also reduced. Seven hours after pupation, there is a 

 greater enlargement of the cerebral ganglia, optic nerves and ganglia, 

 and cords of the future thoracic segments. After twelve hours, the 

 5th pair of ganglia has almost completely coalesced with the cord and 

 the 4th ; at eighteen hours, 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. After 24 hours, the 4th and 

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

 After 86 hours the optic nerves have attained a size almost equal to that 

 of the brain. The 1st suboesophageal ganglion now forms, with the 

 cerebral ones, a complete ring around the oesophagus, the crura having 

 almost disappeared. The 6th ganglion has now disappeared, but the 

 nerves arising from it remain. After 48 hours, 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 

 2nd and 3rd thoracic ganglia have united and the double ganglion 

 thus formed is only separated from the large thoracic mass, composed 

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

 enlarged cords which pass on each side of the central attachment of 

 the muscles. The optic and antennal nerves have nearly attained 



