PHYSIOLOGY OF THE INVERTEBRATA. 325 



The Insecta. 



In these animals there is always a well- developed cerebral 

 ganglion or brain connected by nerve-trunks with a series of 

 ventral ganglia. One of the reasons of the great develop- 

 , ment of the brain is assuredly the greater perfection and 

 the more important ofSce of the organs of the special senses 

 in the Insecta. According 1;o Gegenbaur, many Biptera, 

 Eymenffptera, Lepidoptera, and the large-eyed Libellulce, have 

 powerful cerebral ganglia. The cerebral ganglion or brain of 

 the ants, of bees, and of the spinning spiders (among the 

 Arachnida), is remarkable for its size, and even for its 

 conformation. Though Apis is a much smaller insect than 

 Melolontha, it possesses a cerebral ganglion more highly 

 developed, and relatively three times larger, if we take into 

 consideration the difference of size. The cerebral . ganglion 

 of the ant is proportionally larger still. Besides, the surface 

 of these ganglia or brains is mammillated ; and there are 

 convolutions. According to M. Dujardin,* the brain of Apis 

 has a very singular form. " We perceive a disc with stel- 

 lated striae surmounting like a hood the superior ganglion ," 

 and from certain experiments of M. Paivre,t the cerebral 

 ganglion has, like the cerebral hemispheres of the Vertebrates, 

 the property of being insensible to punctures and lacerations." 



The nervous system of the Insecta (speaking in general 

 terms) consists of a cerebral ganglion connected to a gan- 

 glionated nerve-trunk or trunks, which passes backwards along 

 the ventral surface of the animal. Lateral nerves are given 

 ofE from these ganglia to the organs of sense, limbs, viscera, 

 &c. Fig. 63 represents the nervous systems of various in- 

 sects; and numbers 4 and, 5 of the same figure represent the 

 nervous system of Periplaneta. 



The nervous system of Periplaneta consists of supra- 

 cesophageal ganglia (brain), which are connected by short, 



* Annates des Sciences Naturelles, 1850. 

 t Ibid. 4 s., tomes 8 et 9. 



