BRAIN 



119 



and further that there are a few Insects in which this latter 

 centre is wanting. If the cephalic ganglia and ventral chain be 

 looked on as part of one system, this may be considered as 

 composed originally of seventeen ganglia, which number has 

 been demonstrated in some embryos. 



The anatomy of the supra -oesophageal ganglion is very 

 complex ; it has been recently investigated by Viallanes ^ in the 

 wasp ( Vespa) and in a grasshopper (Caloptenus italicus). The 

 development and complication of its inner structure and of some 

 of its outer parts appear to be proportional with the state of 

 advancement of the instinct or intelligence of the Insect, and 

 Viallanes found the brain of the grasshopper to be of a more 

 simple nature than that of the wasp. 



Fig. 65. — Brain of Worker Ant 

 of Formica rufa. (After 

 Leydig, highly magnified.) 

 Explanation in text. 



Brandt, to whom is due a large part of our knowledge of 

 the anatomy of the nervous system in Insects, says that the 

 supra -oesophageal ganglion varies greatly in size in various 

 Insects, its mass being to a great extent proportional with the 

 development of the compound eyes ; hence the absolute size is 

 not a criterion for the amount of intelligence, and we must 

 rather look to the complication of the structure and to the 

 development of certain parts for an index of this nature. The 

 drone in the honey-bee has, correlatively with the superior 

 development of its eyes, a larger brain than the worker, but the 

 size of the hemispheres, and the development of the gyri 

 cerebrales is superior in the latter. In other words, the mass of 

 ^ Ann. Sci. Nat. Zool. (7) ii. 1887, and iv. 1887. 



