522 



Recently Hooker (: 12) has described histological preparations in 

 which the melanophores of the frog (Rana) apparently lie within ca- 

 vities comparable to the lymph spaces containing the corneal cells. 

 Contrary to the view of Biedermann ('92), he believes that the me- 

 lanophores as a whole may contract and that when this occurs the 

 spaces of the " cavity " surrounding the processes are closed as a 

 result of the intercellular pressure. In addition to the evidence 

 furnished by these preparations, Hooker states that, "Another very 

 strong indication of the fact that the cells expand and contract as a 

 whole is the distribution of the pigment in the expanded and con- 

 tracted phase. In the former, the pigment is uniformly distributed 

 throughout the cell, but owing to the smallness of the diameter of the 



Fig. 2. The same melanophores contracted in a solution containing 4 cc. of 

 0.2 molecular potassium bromide -|- 2 cc. of 0.1 molecular sodium chloride. 



processes and the cell body, the individual rounded granules of pig- 

 ment, are clearly visible. The cell body is never without pigment as 

 represented in the figures of Biedermann for Hyla. In the contracted 

 condition, the pigment is likewise evenly distributed, but, owing to 

 the thickness of the cell body, the individual granules can not be 

 distinguished." Hooker does not discuss the bearing of this concep- 

 tion of the contracting melanophores upon the question of fixed pro- 

 cesses. 



From this brief summary of the experiments it seems probable 

 that the processes of the chromatophores in both crustaceans and 



