OF MANDIBULATA. 44^ 



we must be sensible that however dissimilar the extremes 

 maybe, all these changes are modifications of one principle. 

 But what more particularly deserves remark is, that these 

 extremes should often be visible in neighbouring groups 5 

 nay, in the same order ; that, in short, metamorphosis should 

 differ so much in degree even where the animals are near 

 in affinity. An Orthopterous insect may preserve the same 

 form and habits from the instant it quits the egg up to the 

 period of its death, the only qualities obtained by ecdysis 

 being an augmentation of size and an aptitude to continue 

 the species. But if we turn to the order of Coleoptera, 

 which is contiguous in affinity, it is truly wonderful that by 

 metamorphosis not only the form but the nervous and di- 

 gestive systems may be altered, and the organs connected 

 with these primary functions may all be of a construction 

 different from that which they originally possessed. 



Those changes in the instincts of the same insect which 

 every person must have observed to result from metamor- 

 phosis being considered, it is to be expected that the ner- 

 vous system of the larva and imago will prove different on 

 dissection ; but the difficulty is to understand how any such 

 complete alteration in the nervous system can be effected 

 while the identity of the animal is preserved. The larva of 

 an Oryctes nasicorms, for instance, has, proceeding from 

 the lateral and somewhat posterior lobes of the brain, two 

 nerves, which having embraced the oesophagus consti- 

 tute what may be termed its medulla spinalis, which is 

 here a large fusiform ganglion formed by the agglomeration 

 of smaller ganglions, from which the nerves diverge to 

 supply the various organs. Another pair of nerves which 

 proceeds from the brain, on uniting above the oesophagus 

 forms a small ganglion, which is the origin of a single nerve 



