BIOLOGY. 



[Book vi. 



a disk with stellated striae surmounting like a hood the superior 

 ganglion.^ According to some experiments of M. Faivre, the 

 cerebral ganglion has, like ' the cerebral hemispheres of the 

 vertebrates, the property of being insensible to punctures and 

 lacerations.^ 



Already we can discover in many of the arthropods the 

 existence of a special nervous network, destined for the digestive 

 system. In general, this visceral nervous 

 or sympathetic system springs from the 

 central ganglion by a single trunk. Then 

 it ramifies, and its branches are furnished 

 along their course with small ganglionary 

 enlargements. (Kg. 59, r, r). Dugfes 

 saw this visceral nervous system in the 

 spiders : Andouin and Edwards and others 

 found it in the crustaceans : Lyonnet, 

 Cuvier, Brandt demonstrated its presence 

 in the insects. 



Essentially, and spite of the apparent 



irregularity of its general arrangements, 



the nervous system of the mollushs is merely 



a kind of copy of that of the arthropods. 



„ , . ,. Here we stni find the oSSophagian rinff,' 



QSsopha^au ganglion supe- ^ ^ ^ jr o c 



nor with visceral nervous emitting from its central portion a ganglion- 

 system of a lepidopter . , ^ o o 



(Bombyxmori) ; gs, oephaiio ary peripheric nervous system, distributing 



ganglion superior (cere- . -p ^ _. 



T)roid);a, antennarynerve: itself to the diverse organs, but Without 



0, optical nerve ; r, i/mpair ^ . . , 



tnimh of the visceral nervous regulai'ity, Without Symmetry, as moreover 



system; r'yiherootspringin^ , ^ _ p i i i 



from the cesopiiagicm gang- the general coniormation or the body 



lion swp&rior : s, nerves in ■, ■, -ni t • 



pairs with their ganglionary demands. The SUper-OeSOphagian or cere- 

 enlargements j', f'^ 1-1 ■,. . ,11 11 



oral ganglion is naturally very small 

 in the lamellibranchians which have not a head provided with 

 organs of the senses : it is, on the other hand, very large for 

 the contrary reason, in the cephalophores. 



1 Annales des Sciences Naturelles, 1850. 



? Faivre, Annales des Sciences Naturelles, 4* serie, t. VIII. et IX. 



PiQ. 59. 



