XIV 



CONTRIBUTIONS TO THE BRAIN PHYSIOLOGY OF 

 WORMS 1 



IN his well-known work Ueber Entwicklungsgeschichte 

 der Thiere K. E. von Baer asks how the anterior pair of 

 ganglia of segmented animals should be designated. 



Whether the first pair of ganglia of the segmented animals shall 

 be called a brain or not depends entirely upon the significance 

 which the word brain is given. It is certainly not the organ which 

 we call the brain in vertebrates, for in them it is the anterior 

 extremity of the neural tube, and this is lacking in the segmented 

 animals. It is rather the foremost pair of the series of ganglia, 

 and as the latter is to be compared with the spinal ganglia of the 

 vertebrates the so-called brain of the segmented animals seems to 

 correspond to the Gasserian ganglion of the vertebrates, 2 for the 



latter also receives sensory impulses If , however, one wishes 



to designate by the term brain not a definite organ, but .... 

 that mass of nervous tissue which receives the sensory impulses, 

 then one can, of course, say that insects possess a brain. Only one 

 must keep the meaning of this term in mind. 



He who seeks a definition for the word brain will find 

 the necessary directions in von Baer's remarks. Steiner 3 

 considers it the problem of the physiologist to find such a 

 definition, and has come, apparently without knowledge of 

 the remarks of von Baer, to a different definition which 

 reads as follows : 



The brain is characterized by being the general center of loco- 

 motion in connection with the activities of at least one of the 

 higher sensory nerves Besides its simplicity this definition 



1 Pflilgers Archiv, Vol. LVI (1894), p. 247. 



2 Vol. I (1828), pp. 234 ff. 



3 Sitzungsberichte der Berliner Akademie der Wissenschaften, 1890. 



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