520 



Naclidruck verboten. 



The Mechanism of the Contraction in the Melanophores of Fishes. 



By R. A. Spaeth. 



Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology at Harvard College, No. 241. 



With 3 Figures. 



In spite of the great number of researches that have been car- 

 ried out upon the color-changes of crustaceans, fishes, amphibians 

 and reptiles, little is known of the actual mechanism which effects 

 the migration of the pigment granules within the chromatophores. 

 The older investigators believed that the chromatophores were amoe- 

 boid cells in which pseudopodia-like processes were projected into 

 the surrounding intercellular spaces. In the contracted phase these 

 were supposedly withdrawn. Subsequently it has been claimed 

 (Ballowitz, 93 and others) that the processes are not withdrawn, but 

 that the pigment granules move distally and proximally within them. 

 There has thus arisen the question: Do the pigment granules migrate 

 in and out of fixed processes or are these changeable and to be com- 

 pared with the pseudopodia of the amoeba? 



Keeble and Gamble ( : 04) found that in Macromysis flexuosa, 

 ''Repeated experiments of stimulation on the same chromatophore 

 cause it to contract to the same centre, and to expand into the same 

 branches, and so produce the same pattern. These chromatophore- 

 endings, however, are frequently so intricate as to give rise to the 

 appearance of a plate of pigment, for example, on the eyestalk and 

 on the surface of the tail. In such cases it is difficult to determine 

 whether the structure is the same as that just described for the main 

 trunks, or whether the branches ultimately end in connection with a 

 system of tubes". 



ÜEGNER (:12) observed the changes in the dorsal chromatophores 

 of a living Praunus flexuosus. Owing to the constant vibrations of 

 the animal photographs could not be made of successive expanded 



