250 Journal of Comparative Neurology. 



oriparous tubes is irrelevant, since in this case the contraction and ex- 

 pansion is in no way different from that in other muscular tissue. The 

 difficulty seems to be that there is no definite criterion set up as to the 

 meaning of the term "amoeboid movements." Going back to the 

 typical case of the amoeba or leucocyte, it would appear that amoe- 

 boid movements must mean the extension and retraction of portions of 

 the cell substance —an actual change in form and not merely of the 

 interior parts of the cell. These changes are very different from those 

 which are described as occurring in the case of the tissues mentioned 

 above. True amoeboid movements mean changes in which the 

 branches of the cell lengthen and shorten. The cells involved in the 

 growth of cicatricial tissue are leucocytes, so that they furnish no new 

 evidence for the theory. So far as it goes the evidence from the leuco- 

 cytes, of course, is positive. 



The next evidence is found in the facts concerning movements in 

 the retina. These movements are claimed for two types of cells, first, 

 for the pigmentary cells and for the rods and cones, and second, for 

 the internal granular layer of bipolar bells and for the ganglionic layer 

 of multipolar cells. Taking up first movements in the distal part of 

 the retina, Deyber begins by referring to the researches of Boll (15 and 

 16) in 1877, who noticed that under the influence of light there was a 

 change in the state of the pigmentary and rod and cone layers. These 

 changes are interpreted as follows : Under the influence of light the 

 pigmented pseudopodia of the pigment cells penetrate as far as the 

 outer limiting membrane, while in darkness they retract, leaving un- 

 filled spaces where they had been. Kuhne (53) made similar observa- 

 tions. Angelucci {2) in 1878 showed in the frog that the limit reached 

 by the pigment in darkness was the external third of the rods. In 1884 

 he demonstrated that the pigmentary cell diminished in size under the 

 influence of light, contracting in its width at the same time that the 

 distal part of the rods became thicker. Angelucci himself be- 

 lieved this to be due to a migratory movement of the pigment within 

 the cell. Van Genderen-Stort (41) observed, in 1884, a migration of 

 the ellipsoids of the cones in darkness from their position next the 

 outer limiting membrane to a position on a level with the external third 

 of the rods. A little later, in 1887, he demonstrated (42) the contrac- 

 tion of cones under the influence of light. In 1885 Gradenigo (43) 

 showed that the external granular layer undergoes changes. The 

 nuclei in darkness become rounded; in light elongated. This is accom- 

 panied by a contraction of the internal part of the rods. In 1887 

 Denissenko (29) noticed that under the influence of light the entire 



