614 K, H. J. SCHFSTEK. 



legist is the mapping' out of the cortex iuto areas dilfering' 

 from one another in strncture. In doing- this he may take 

 into account the form and arrangement either of the nerve- 

 cells or of the nerve-fibres, or he may divide the sui'face into 

 regions distinguished by the period at which they arrive at 

 maturity. In an exhaustive treatment of the subject evidence 

 obtained in all these ways must be considered and co-ordinated 

 — a difficult task, since the interpretation of the observations 

 is beset with pitfalls, and in consequence a number of apparent 

 inconsistencies have to be explained away or harmonised. 



On some points already a considerable degree of certainty 

 has been nrrived at, namely the extent of the area concerned 

 directly with the movement of tlie voluntary muscles, and of 

 that region in which the visual impulses set up in the retina 

 reach the cortex. With regard to these points the evidence 

 from all sources is in agreement, and the definite function is 

 in each case correlated with a perfectly definite structure, 

 which, particularly in the case of the visual area, sharply 

 delimits it. A perfectly definite structure also marks the 

 olfactory cortex, while to many other structurally distinct 

 areas a special function may be assigned with some degree 

 of confidence. 



That a better appreciation of a physiological and anatomical 

 problem may be obtained by extending it into the realms of 

 comparative physiology and comparative anatomy is generally 

 accepted. Both the points of agi-eement and the points of 

 divergence in structure between animals with different habits 

 living in different environments may elucidate the relation 

 between structure and function. The present paper aims at 

 making a small but definite contribution to the subject, in 

 that it consists of a description of a special aspect of the 

 histology of the cortex in an animal not hitherto treated in 

 this way. The histological study of tlie cortex may be 

 pursued in at least three different ways. Firstly, the nerve- 

 fibres may be stained by some method like that of Weigert ; 

 secondly, the nerve-cells may be stained either by the Golgi 

 or Cajal process. These are uncertain in action and only 



