158 REFLEX ACTION AND 



Reptile, and other Vertebrates, the separate ventral gan- 

 glia of the Centipede are represented functionally by a 

 continuous cord-like aggregation of fused centres, which 

 occupy the median line in the dorsal aspect of the body. 



The lower the organism, the more independent is the 

 functional activity of its several nerve ganglia, while the 

 higher the animal in type and scale of organization, the 

 more closely knit together are the activities of these several 

 parts of the nervous system. Even in Man himself, how- 

 ever, we have frequent evidence of the independent action 

 of more or less limited regions of the nervous system. 

 This is the case, for instance, in winking, sneezing, 

 coughing, swallowing, which are all of them reflex or 

 ' automatic ' actions. The latter name has been given on 

 account of the machine-like regularity with w T hich such acts 

 are performed independently of all conscious guidance. 



The existence and mechanism of ' reflex actions ' were 

 first distinctly referred to by David Hartley in 1748 ; they 

 were more definitely described by Prochaska in 1784 ; 

 though it was Marshall Hall who, some fifty years later, 

 first clearly recognized and elucidated their real impor- 

 tance. Since his time our knowledge of these actions has 

 been widened in all directions by the labours of many 

 physiologists. 



The fact that each Ganglion in. one of the lower 

 animals constitutes an independent centre for reflex 

 actions, and that the movements to which it gives rise are 

 always co-ordinated and adaptive in their characters, was 

 experimentally established by Duges. 



This naturalist made some interesting observations on 

 the ' Mantis,' a large insect having some resemblance to a 

 Cricket which is very common in the south of France and 

 in Italy. The creature is notable for a long, narrow, first 

 thoracic segment, to which are attached a pair of large and 



