298 RESEARCHES ON CORTICAL LOCALISATION AND 



absolute development) a sufficient cerebral cortical mechanism for the 

 performance of these lower associations. The actions which are the 

 outcome of such associations are often complex, and as an instance 

 of the class included under this heading the tunnelling of the mole 

 may be mentioned. Such more or less stereotyped actions may show 

 signs of improvement in their performance, firstly, as the result of 

 perfection by use of an inherited mechanism, and secondly, as the 

 result of the intermingling of activities for which it is concluded that 

 the supra-granular layer is responsible. In the latter case, however, 

 the actions would merge into those which are more properly described 

 as habitual intelligent, or into the class of ' incomplete instincts ' 

 (Lloyd Morgan), or ' mixed instincts ' (Romanes)." 



Watson finally remarks, on the subject of the functions of the 

 " supra-granular " (outer cell layer) and " infra-granular " (inner 

 fibre layer and inner cell layer) : 



" In practical animal behaviour the two sets of processes are pro- 

 bably more or less constantly interwoven, the higher activities (supra- 

 granular layer) coming to the aid of the lower as far as the capability 

 of the animal allows. In the case of the lower mammals (e.g. insecti- 

 vora) the limits of this capability are comparatively soon reached, 

 and correspondingly these mammals possess a relatively poor supra- 

 granular layer. Many of these lower mammals have adopted a safe 

 mode of life, others have resorted to fecundity. With these, which 

 may, for present purposes, be termed extraneous aids to survival, 

 their essentially instinctive activities have been relatively sufficient 

 to ensure their continued existence. There has, therefore, in these 

 mammals, been little necessity for the development of a supra-granular 

 layer, the infra-granular portion of the pallium providing most of the 

 necessary cortical physical basis required for practical behaviour. 



" The infra-granular layers, with the reservation to which refer- 

 ence has been made, thus constitute the earlier developed and more 

 fundamental associational system of the cerebral cortex ; the supra- 

 granular layer, a higher and accessory system superadded, and of 

 any considerable functional importance only in certain regions in 

 lower mammals, such as the insectivora." 



Before the question of cortical localisation receives attention, an 

 important communication by Mott (1904), on the progressive evolu- 

 tion of the structure and functions of the visual cortex in mammalia, 

 calls for reference, as a prominent feature of the article is the con- 

 sideration paid to the cell lamination of the visuo-sensory and visuo- 

 psychic regions. The paper deals with the subject from not only 



