MELANOPHOKES OF HANA 248 



preparations thMiioiistrate the cell as a soiiunvhat oviil mass of 

 pigment surrounded by a thin layer of cytoplasm and occupy- 

 ing a cavity which is apparently much smaller than that in which 

 the expanded cells lie. Careful observation, however, brings out 

 the fact that the ca\'ity has no less volume than before, but 

 that, with the contraction of the melanophore and the accom- 

 panying concentration of its cytoplasm, the superficial and deep 

 walls of the cavity have collapsed peripherally, while in the cen- 

 ter, which is now the only part occupied by the cell, these walls 

 have been forced further apart. This has produced, in place of 

 the flat-surfaced cavity, one with convex superficial and deep 

 walls. Seen from the surface, the focal plane of the microscope 

 cuts the rounded u])i)er wall of the cavity and gives the impres- 

 sion of a fairly well-defined ring. 



MELANOPHORES OF THE ADULT 



In the adult frog, the corial melanophores are found in the 

 skin just below the fixed yellow pigment cells, the xantholeuco- 

 phores, which, in turn, lie directly beneath the epidermis. In 

 the expanded phase, the processes of the melanophores lie nearly 

 at right angles to the cell body, surrounding the xantholeuco- 

 phores. This fact, together with the thickness of the skin, ren- 

 ders minute examination of the living melanophore very difficult. 

 The web of the foot was chosen as the most favorable jilace to 

 examine these cells in the living frog. 



In an attempt to overcome some of the difficulties experienced 

 in the study of the melanophores in the live frog, pieces of skin 

 and portions of the web were mounted in plasma according to 

 Harrison's method.'' While some additional details could be thus 

 observed the results were not as satisfactory as had been hoped 

 for, though, for other purposes, such preparations are excellent. 



The stud}^ of li\'ing adult melanoi^hores, l)oth in \'ivo and in 

 vitro, demonstrates that each cell has its own pattern which it 

 assumes whenever fully expanded. This fact has been noted by 



^ A description of this method and its modifications will Ix- found in the fol- 

 lowing papers: R. Ci. Harrison, 1910, Jour. Exp. Zool., vol. 9, i). 7'Jl; M. T. Bur- 

 rows, 1911, .lour. Exp. Zo(')l., vol. 10, pp. (i6-69. 



