INSECTA. 365 



nerve is continued of equal breadth, so as to seem rather as a lobe of 

 the brain. It expands, and, like the stalk of a mushroom, forms the 

 stem of a very large reniform ganglion, the convexity of which is 

 turned forwards and outwards, and the free concave projecting 

 margin developed at the under part. Thousands of branches to the 

 divisions of the compound eye are given off from the convex surface 

 of this ganglion. The brain presents a single median inferior lobe ; 

 the oesophageal chords sent downwards to the maxillary ganglion are 

 short and thick. This ganglion is succeeded by three large equi- 

 distant thoracic ganglia, of which the last two, corresponding with 

 the elytral and alar ganglions of the preceding insect, are, as might be 

 expected, from the development of the muscles of the wings (both of 

 which are alike organised for flight), considerably the largest. Of 

 the ganglia of the abdomen, the terminal one resulting from the con- 

 fluence of two, and which supplies the organs of generation, is 

 remarkable for its large size. 



In the white butterfly {Papilio hrassiccB) the brain is a thick trans- 

 verse rounded mass, indented by a longitudinal furrow along the 

 median line. From its sides proceed the large optic nerve, now greatly 

 surpassing the other cerebral nerves in size. The oesophageal collar 

 is triangular, leaving a very small interval for the passage of the 

 alimentary gullet. The maxillary ganglion is relatively much smaller 

 than in the dragon-fly, the blatta, and other mandibulate insects. 

 The first two thoracic ganglions are blended into one, and the third 

 tlioracic and first abdominal ganglions have coalesced to form a 

 similar mass in the thorax, connected with the preceding by short 

 chords, separated by an interval to allow the passage between them 

 of certain processes of the thorax giving attachment to the muscles of 

 the legs. The ganglions of the thorax have been observed in some 

 species (as the Bomhyx Neustria) to present a reddish tint. They are 

 succeeded in the Lepidoptera by four other ganglions in the abdomen, 

 of which the last, as usual, is the largest. 



The nervous system of the chaffer {3Ielolontha) has been dissected 

 and delineated by Strauss* with a minuteness and accuracy second 

 only to those of Lyonnet. In his beautiful plates are shown the 

 bilobed brain with its auxiliary ganglia for the eyes and antennje ; 

 the stomato-gastric nerves and their small lateral cephalic ganglia 

 are also clearly exhibited. The sub-oisophageal or maxillary ganglion 

 is of an oblong form ; the brachial ganglion is triangular ; the elytral 

 ganglion is of a circular, and the alar ganglion of a pyriform, figure ; 

 these two latter being concentrated into almost a single mass, and 



• CCXLII. 



