448 J. ariAHAM kerr. 



during tlieir retraction, after the manner familiar to any one 

 who has watched living Foraminifera. 



Circumstances, unfortunately, did not allow of my making 

 any experiments as to whether a nervous reflex plays any 

 part in the contraction of the chromatophores. I am inclined 

 to think, however, that we have to do with a direct action of 

 light upon the individual coll. 



I wish to draw attention to one point ; that there is a 

 fundamental similarity in the reaction to light stimulus of the 

 general chromatophores of the body and the cells of the 

 2)igment layer of the retina. In both we have to do with 

 relatively slightly differentiated cells, and in both their 

 reaction to light (in addition probably to the formation of the 

 pigment itself) consists in their pushing out positively lielio- 

 tropic pseudojDodia. 



General Morphology of the Fore-brain Region, 



It is fashionable to accept the view that the "secondary 

 fore-brain " is fundamentally an unpaired structure, forming 

 topographically the anterior end of the ccrebro-spinal axis of 

 the adult — that it is a " telencephalon." 



It will be seen that the conditions holding in the ontogeny 

 of Lepidosiren go completely against this view. On the 

 ccmtrary, they su])port the opposite and older view, the view 

 held by von Baer, Reichert, Goethe, and in recent times 

 including as one of its chief exponents Studnicka, that the 

 hemispheres arc fundamentally paired bulgings outwards of 

 the lateral wall of the thalamencephalon, of a nature roughly 

 comparable with the outward bulgings which give rise to the 

 eyes. The portion of brain from which they project out- 

 wards is simply the anterior portion of the original fore- 

 brain,' which, as has been shown, becomes mai'kcd off at a 

 very early period of development by an upward bend in its 

 floor, — that is to say, it is simply and solely thalamence- 

 phalon. 



' Vorbini of Kupffcr. 



