C44 Edgar Davidson Congdon 



Parker found a migration of the accessory pigment, but as it is 

 not easy to determine this even in its relation to the hght, I did not 

 occupy myself with its relation to heat. 



Ill CAMBARUS BARTONII GIR. 



In the crayfish Cambarus bartonii the reaction of the retinal 

 pigment to changes in light and in temperature were by no means so 

 clear as in the prawn. Exner ('91, pp. 108-109) long ago made a 

 similar statement about Astacus, so far as light reactions were con- 

 cerned. 



In experimenting on Cambarus the factor of light was elimin- 

 ated by confining the temperature treatment to animals in the dar^. 

 The series of temperatures tested was 2°, 10°, 14°, 22°, 29°, 34°, 

 39° and 41° C. The high temperatures 39° and 41° C. resulted in 

 the death of half the animals and produced variable conditions 

 in the eyes of the survivors. The experiments were discarded as 

 probably dependent upon irregular moribund conditions. There 

 was no reason to think that 2° C. was harmful. As a precaution 

 against shock the more extreme temperatures were only gradually 

 applied. Animals that were subjected to 2° C. were kept at this 

 temperature for twelve hours, so that, if the cell processes were 

 somewhat retarded by the cold, sufficient time would be given 

 for the reaction to become complete. The animals were kept at 

 the other temperatures for at least two and a half hours, as in 

 the case of Palaemonetes. The low temperatures were obtained 

 by putting the animals in a shallow dish supplied by water 

 cooled by ice. For the high temperatures, a tank was arranged 

 in a light-proof box so that water of a desired temperature 

 could be replenished without admitting light. After the experi- 

 ments the eyes of the animals were fixed in water at 80° C. The 

 tough cuticula was then removed and the retina sectioned and 

 stained in borax carmine. 



The distal retinular cells of Cambarus showed in the different 

 experiments a considerable diversity of positions and could not be 

 reduced to a simple series conformable to the differences of tem- 

 perature. I am inclined to ascribe this condition to some fault in 



