294 Journal of Compavativc Neurology and PsycJwlocry, 



Part II. The Cf.ntrai, Nkrvous System of the Guinea Pk;. . 341 



Introdurtion. . . . . . . . . . 341 



/. Description of Transverse Sections Throttgh the Medulla Spinalis 



of the Guinea Pit; at Birth. ...... 343 



Cervical 343 



Thoracic. ........ 345 



Lumbar. ......... 345 



//. Deiiclopmeni of the Medulla Spinalis from Birth to Maturity. 347 



Cervical. ......... 347 



Thoracic. ........ 349 



Lumbar. ...... ... 350 



Summary of changes in medullalion of the medulla spinalis. 3^0 

 Increase in area of cross-sections of the medulla spinalis 



from t)irth to maturity. . . . . . -55 1 



///. The Encephalon of the Guinea Pie;. . . . . . 353 



Cerebrum. . . . . . . . -'SSl 



Development of the cerebral hcmisjilieres. . . 35^ 



Cerebellum. . . . . . . . . 3:^6 



Increase in the area of cross-sections of the encejihalon. 357 

 /v. Comparison Betiveen the Nervous System of the Guinea f'li;- 



and that of the White Rat. ..... 358 



INTRODUCTION. 



In the study of animal psychology the atteni pt is made to 

 understand in their simplest manifestations the psychical fac- 

 tors entering into reactions to stimuli. 



With this in view reactions of all grades of intelligence 

 have been investigated. Two different points of view have 

 given opposing interpretations of the phenomena manifested by 

 the lower animals. 



M. Binet' has observed the reactions of Paratticcia to 

 acids and alkalis, and has concluded " that an action of adapta- 

 tion involves spatial perception of the external object, choice 

 between objects and movements of approach or avoidance. 



On the other hand, Jennings ' gives a physio-chemical ex- 

 planation of these same reactions. All the movements of ap- 

 proach and retreat are automatically performed without regard 

 to the "pleasure" or "pain" involved. The mechanism of the 



' JjINET. Psychic Life of Micro-organisms. Transl., Chicai;o, Open Court 

 Pub. Co., 1889. 



■'■ P. 61. 



■MI. S. Jenmnc.s and E. M. Moore. Studies on Reactions to Stimuli 

 in I'nicellular Organisms, \^III. Amer. Jour, /'hysiol.. Vol. VI, 1902. 



[ 2] 



