1913] Holmes: Pigment Cells from Larcae of AmphihiaHs 145 



when they happened to eome in contact with the cover slip from 

 which the culture was suspended. Sometimes the connective 

 tissue cells migrated out along the surface film of the lower side 

 of the drop, but in no case were the pigment cells observed to 

 creep outward unless they came into contact with the glass. The 

 isolated position of the pigment cells presents an exceptionally 

 favorable opportunity for the study of their structure and 

 movements. While these cells are in their natural situation 

 within the tissues of the body it is often possible to see very 

 clearly the distribution of their pigment, but next to impossible 

 in most cases to follow the outlines of the cells themselves. The 

 uncertainty that has so long prevailed in regard to the move- 

 ments of chromatophores is largely the result of this difficulty. 

 When the pigment cells accommodatingly isolate themselves, and 

 get out where one can get a good look at them with all powers 

 of the microscope, and then exhibit characteristic changes in the 

 distribution of their pigment, the difficulties of observation are 

 practically all cleared away. 



The observations on Hyla were made upon embryos nearly 

 ready to come out of the .jelly, and upon larvae that had recently 

 emerged. After a short treatment with weak hydrogen peroxide 

 solution (a stronger one is soon fatal) the embryos or larvae 

 were placed in sterile Ringer's solution and cut into small pieces. 

 A single piece was then placed in a hanging drop of the culture 

 medium, and sealed up in a hollow slide. Pieces put up in 

 Ringer's or Locke's solution, while they lived several days and 

 showed more or less outwandering of cells, failed to afford any 

 good cases of active migration of chromatophores, nor did the 

 chromatophores while in the tissues present as natural and 

 healthy an appearance after a few days as pieces put up in 

 plasma or serum. Owing probably to the weak antiseptic solu- 

 tions that could be used without injuring the animals, prepara- 

 tions in Ringer's or Locke's solutions were frequently infected by 

 bacteria, while such contamination was much less common in 

 preparations made with fluids from the blood. 



Preparations in plasma showed in several cases, but by no 

 means in all, a wandering out of a few pigment cells from one 

 to three days after being mounted. The different pigment cells 



