132 



HYPOTHESIS OF THE DEVELOPMENT OF 



penter.} We see clearly that there has been a succession from 

 invertebrate to vertebrate ; then, in the vertebrate, from the 



FIG. 75. 



B 



E 



Successive Stages of Development of the Human Brain. 

 A., at the 7th week ; a, rudiment of hemispheres ; b, corpora striata; c, 

 corpora quadrigemina ; d, cerebellum: B, at the Yithweelc: C, at 

 the 15th week; e, optic thalamus: D, at the 2,1st week : E, at the 

 27th week. In the relative proportions of the principal parts of the 

 Human Brain at these successive periods, there is a very close corre- 

 spondence to the proportions presented by the corresponding parts of 

 the Brains of Fishes, Reptiles, Birds, and the lower Mammalia. 



fish to the reptile, from the reptile to the bird and mammal ; 

 in the mammal, finally to man. That there has also been an 

 advance in each stirps or series of animals, is abundantly evi- 

 dent. In connexion with advance of grade, there appears to 

 have been a progression from general to special characters. It 

 has been pointed out that the Cystidea, an early echinoderma- 

 tous form, presents "a combination of the distinctive cha- 



