Chap, i.] THE NERVOUS SYSTEM IN THE ZOOLOGICAL SERIES. 369 



The visceral nervous system of the mollasks, is like their 

 general nervous system, a copy of that of the arthropods. 



On the other hand the cerebral ganglion of certain cephalopods 

 has affinity in some respects with the brain of the vertebrates. 

 There exists in these animals a cephalic cartilage, forming a sort 

 of cranian cavity, and hollowed with a f ossette destined to be 

 occupied by the cerebroidal ganglion. This cartilage is the 

 rudiment of an orbit and lodges the organs of hearing. 



The super-cesophagian ganglion of the moUusks seems also to 

 have special functions. If we remove this ganglion in tl^e snail 

 the animal survives the operation four or five weeks, but remains 

 completely without movement. On the other hand, the extirpa- 

 tion of the sub-cesophagian ganglion kills the animal in twenty- 

 four hours. 1 



The excitation of the cerebroidal ganglion of the moUusks 

 produces little or no effect. It is the same with its galvanisa- 

 tion. But the case is altogether different with the sub-cesophagian 

 ganglion. Its irritation provokes a vigorous muscular agitiation : 

 its galvanisation by the continuous currents has often for effect 

 to stop the heart in its state of dilatation, or of diastole, exactly 

 as happens with the galvanisation of the pneumogastric nerves 

 in the vertebrates. 



These facts tend to confirm the opinion of the German evolu- 

 tionists, who wish to connect genealogically the vertebrates with 

 the mollusks. However, if we take into account nothing but the 

 general conformation and distribution of the nervous system, the 

 analogy, remote though it may be, exists rather between the arthro- 

 pods and the vertebrates. In effect the nervous system of the 

 acranian vertebrates can be strictly considered as a very co- 

 alescent ganglionary nervous system. The most imperfect of the 

 acranian vertebrates, the amphioxus, has as central nervous system 

 merely a nodose spinal marrow, that is to say, offering a series 

 of enlargements, each of which corresponds with the origin of a 



^ Vulpian, Le(ons sw la Phynohgie GiniraU et Comparie du SysUme 

 Neniewx, pp. 757-761. 



B B 



