Bawden, Movements of the Neurone. 251 



retina became thicker as a result of the enlargement of the space occu- 

 pied by the external and internal granular layers. Mann (66) in 1894 

 in his researches on the dog discovered that the nuclei of the rods of 

 the eye kept in darkness were diminished in volume and rich in glob- 

 ules of stainable substance situated in the periphery of the nucleus. 

 On the other hand, after the action of light, this substance appeared 

 concentrated toward the centre of the nucleus, presenting a star-like 

 form. The recent experiments of Pergens (81), in 1896, confirm the 

 work of Kiihne, Angelucci and Gradenigo. His experiments were 

 made on the eyes of a physostomous teleost, Leuciscus rutilus. Two 

 lots of fishes were isolated, one in total darkness for 48 hours and the 

 other in continuous light. At the end of this time they were killed and 

 subjected to the same treatment. The figures that Pergens gives, as 

 interpreted by Deyber, show that the pseudopodia of the pigment cells 

 of the fishes that were kept in the dark are short, while in the other 

 eyes the pseudopodia are long, penetrating deeply among the rods and 

 cones. Along with this prolongation of the pigment cell is noted a 

 contraction of the protoplasmic portion of the rods and cones. In the 

 external granular layer Pergens found that the nuclei became elongated 

 in darkness. Under the influence of light, on the other hand, there 

 is a retraction of the protoplasm which re-enters in part mto the exter- 

 nal granular layer through perforations in the outer limiting membrane, 

 Pergens also found movements in the internal granular layer of bipolar 

 cells and in the ganglionic layer of multipolar cells in which the char- 

 acter of nerve cells is best preserved. Certain of the older investiga- 

 tors also found changes in this part of the retina, but their results are 

 more or less conflicting. Since these changes are of the same charac- 

 ter as those referred to below in the case of the true cortical neurones, 

 no further citation of the researches is necessary. 



Two criticisms may be made upon these results : (i) touching the 

 argument in so far as it rests on the supposed movements of the pig- 

 ment cells, and (2) the argument in so far as it rests upon the compari- 

 son of the tissues prepared in the hght and darkness respectively. The 

 second point involves the relation of the reagent used to the state of 

 the tissue as affected by its activity. This will be taken up below. 

 With reference to the first point, the sufficient reply to the argument, 

 (in so far as these changes are not also amenable to the criticism which 

 we are reserving until we come to speak of the neurone), in so far as it 

 is based on changes in the pigment cells, is that recent researches ren- 

 der doubtful the inference that there is any true amoeboid movement 

 in these cells. The fact is, as brought out for Crustaceans in a recent 



