MOVEMENTS IX THE VISUAL CELLS 137 



on dull days maximal expansion in the light was hard to obtain. 

 Among fishes in general, more doubtful cases occurred in ex- 

 periments conducted in the dark than in the light, yet in all 

 such cases the uncertainty merely lay in deciding between two 

 nearly equal conditions, while in practicalh' no instance was there 

 evidence of a definite reversal whereby a greater distal migra- 

 tion occurred at 25°C. than at 5°C. 



2. Fundulus. The conclusions reached from the study of 

 Fundulus, as well as from the other fishes, are similar to those 

 given for Ameiurus, but each fish shows individual peculiarities 

 in the disposition of the pigment and these will be briefly 

 described. 



In the light the pigment of Fundulus tends to migrate to a 

 great extent forming a broad zone at the distal ends of the cells, 

 much denser and more sharply defined than in Ameiurus. Be- 

 tween this zone, which has a width of 30 m, and the bases of 

 the cells there is a clearer area, almost devoid of pigment at 

 5°C. (fig. 5), while at 25°C\ (fig. 0) this region contains a con- 

 siderable amount of evenly distributed pigment granules. In 

 the latter case, however, the pigment still forms a closely aggre- 

 gated zone distally, although it is reduced to a width of 17 m- 

 As in Ameiurus the condition at lo°(\ more closely resembles 

 that at 25^C. than at 5°C. 



A peculiarity in preparations of the light-adapted retina of 

 Fundulus (at least with Perenyi's fixation) is that at the higher 

 temperatures the pigment extends in columns from base to 

 periphery of individual cells (fig. (i), while between such columns 

 of adjacent cells are elongated areas free of pigment but taking 

 the plasma stain. Examination under high magnification does 

 not show the presence of excessive shrinkage, although a casual 

 observation might suggest that this had occurred. AMiere the 

 pigment is aggregated at the base and periphery of the cells, 

 cell boundaries are not distinguishable and the pigment appears 

 as homogeneous masses. The separate columns connecting these 

 two continuous zones give the whole an appearance not imlike 

 a ladder with rungs set very close together. 



THE JOt'RNAL OF COMPAKATIVE NEUROLOGY, VOL. 26, NO. 2 



