516 



KerrI), that there is no necessity for me to give any general de- 

 scription of the phases of developraeut of the organ as a whole. So 

 that I can at once plunge into the account of the special points that 

 have a bearing on the cerebral cortex. 



The illustrations in Burckhardt's memoir 2), not to mention the 

 work of several earlier writers, have made us acquainted with the form 

 of the brain in Protopterus, which closely resembles that of Lepidosiren ; 

 and Graham Kerr has pointed out the ditferences which distinguish 

 the one from the other. 



Fig. 2. A photograph of the same section, including the right hemisphere also. 



It was very unfortunate that Burckhardt's investigations were 

 undertaken at a time when little was known concerning the structure 

 of the brain in the Monotremata and Marsupialia, because the infor- 

 mation derived from the study of these lowly mammals gave us the 

 clue for the identification of the various cortical areas in the non- 

 mammalian vertebrata. The importance of instituting exact homologies 

 with the mammahan organ largely depends on the fact that most of 



1) The Development of Lepidosiren paradoxa. Part 3. Development 

 of the Skin and its Derivatives. Quarterly Journal of Microscopical 



Science, Vol. 46, N. S. 



2) Das Zentralnervensystem von Protopterus annectens, Berlin 1892. 



