338 Journal of Comparative Neurology and Psychology. 



IV. Dcvelopiiioit of the Gtiinca Pig Couiparcd iviili that of 



the White Rat. 



Guinea Pig. 



Weight: Varies greatly at birth. Av., 

 female, 70. 8 gr.; male, 70. 1; Adult, 

 f., S00.5 ; m., 776.9 gr.^ 

 Senses: Eye functions fully at birth. Opens 16 to 17 days. 



Ear functions at birth. Functions fully after 13th day. 



Touch never very sensitive. Sensitive around the mouth, other" 



wise dull. 

 Smell perfect at birth. Sensitive at birth. 



Taste perfect at birth. Present, but no differentiation be" 



tween pleasant and unpleasant. 

 Body : Thoroughly covered with fur ; Naked, ill-developed, immature in form 

 complete muscular development ex- and musculature, 



cept the hind legs. 

 Nervous system : practically completely No medullatipn at birth. 



medullated. 

 Spontaneous movements not numerous Movement very slight and weak at 

 but strong at birth. On second day birth, and does not attain vigor un- 



movements very numerous. til fifth day. 



Coordination : imperfect for first three The few movements attempted are co- 

 days but perfect thereafter. ordinated, and after learning to crawl 



(from 4th day* coordination rapidly 

 increased. 

 Random movements : increase in num- Increase in number and vigor from 4th 

 ber from 2 to 8 days. About constant to 60th or 70th day. 



throughout maturity. 



Psychical Development. 

 Instincts : almost fully functioning at Instinctive reactions are characteristic 



birth. of life up to 12th day. 



Memory : proved to be present at sec- Develops soon after lOth day. Perfect 



ond day. Perfect at -\ days. at 19 days. 



Psychical maturity : 3rd day. 23 to 27 days. 



The data for the white rat are derived from the records of Small ^ and 

 Watson. 3 



' MiNOT. Senescence and Rejuvenation, foiim. Physio!.. Vol. XII, p. 131. 

 ■^ .AmeT^. Jozir. Psychol , Vol. XI, pp. So-ioo. 

 ■^ Animal Education, Chicago, 1903. 



[46] 



