368 



BIOLOGY. 



[BOOK vi. 



a disk with stellated strise surmounting like a hood the superior 

 ganglion. 1 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. 2 



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. (Fig. 59, r, r'). Duges 

 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 mollusks is merely 

 rQ a kind of copy of that of the arthropods. 



Here we still find the oesophagian ring, 



(Esophagian ganglion supe- 

 rior with visceral nervous emitting from its central portion a ganglion- 

 system of a lepidopter 



s, cephalic ary peripheric nervous system, distributing 



nglion superior (cere- ., -A , ,, ,. , , .,, 



broid);a, antennary nerve : itself to the diverse Organs, but Without 

 o, optical nerve ; r, impair ., 



trunk of the visceral nervous regularity, without symmetry, as moreover 



system; r 1 , the root springing , , . .. . , 



from the assophagian gang- the general conformation of the body 



lion superior ; s, nerves in. -, , m ., i 



pairs with their ganglionary demands. The super-cesophagian or cere- 

 ts ',*". kj.gj g an gii on j s 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 Anndles des Sciences Naturelles, 1850. 



2 Faivre, Annales des Sciences Naturelles, 4<* serie, t. -VIII. et IX. 



