CHAP, i.] THE NERVOUS SYSTEM IN THE ZOOLOGICAL SERIES. 367 



nervous enlargements, takes place in the arachnida, the insects 

 (Fig. 57), the crustaceans. The cerebral ganglion and the central 

 chain of these last sometimes fuse into a single mass, whence 

 radiate the nervous cords (Fig. 58). This mass is merely divided 

 into two parts by the foramen, the cesophagian ring. 1 There is 

 here a degree of concentration of the ganglionary cells, greater, 

 in some respects, than in the vertebrates themselves. It is one 

 of those paradoxical facts which show how far from absolute our 

 pretended biological laws are. Nervous concentration, which we 

 have accustomed ourselves to consider one of the signs, of the 

 means, and of the results of organic perfectionment, is better 

 realised in the crustaceans than in man. 



There is, however, another law which does not seem to suffer 

 exception ; it is that of the predominance, greater and greater 

 of the cerebral ganglion, in proportion as the intelligence is 

 developed. One of the reasons of this development is assuredly 

 the greater perfection and the more important office of the 

 organs of the special senses, forasmuch as certain crustaceans, 

 for instance the large-eyed amphipods, have a very voluminous 

 cerebral ganglion, lobed, and emitting optical nerves. In like 

 fashion, and for the same reason, the large-eyed libellulas, many 

 dipterans, hymenopters, the lepidoptera (Fig. 59 g s) have a 

 powerful cerebroidal ganglion. 2 Nevertheless the degree of de- 

 velopment is closely related to the volume of the cerebral 

 ganglion. The brain of the spinning spiders, of ants, of bees, is 

 remarkable for its volume, and even for its conformation. 

 Though the bee is much smaller than the cockchafer, it possesses 

 a brain much more developed, and relatively three times larger, 

 if we take into consideration the difference of size. The brain 

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

 these cerebroidal ganglions so much developed is mammilated ; 

 we find there bourrelets, something analogous to what are cir- 

 cumvolutions in the brains of the vertebrates. In the bee, accord- 

 ing to Dujardin, the brain has a very singular form. We perceive 

 1 Gegenbaur, loc. tit., p. 348. a Ibid. 



