42 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



selves, owing to the irritation produced by the intruding parasite, have 

 developed pigment granules in their interiors, and become like pigment 

 cells in optical character. Specimens of the cornea cleared in glyce- 

 rine show this criss-cross arrangement of pigmented x>lasma, embedded 

 somewhat like the warp and woof of a loosely woven kind of cloth in 

 the clear corneal substance. More usually, however, the pigment cells 

 are unmodified chromatophores, especially where they lie superficially 

 and do not fall under the influence of the corneal lacunas normally in- 

 habited by the corneal corpuscles, where they of course would have 

 their shapes modified to correspond with the form of the bodies which 

 they have replaced. 



I have for a long time known that the chromatophores or pigment 

 cells of fishes have a certain power of movement among the cells of the 

 skin, especially of embryos, and that they not only slowly change their 

 form but also their positions by means of what cannot be regarded as 

 other than a special kind of independent amceboid migratory movement. 

 In this way their modes of aggregation are slowly altered, while an act- 

 ual growth and extreme flattening occurs in the course of development, 

 during which they seem to cover more space than at first, and I am 

 very doubtful as to whether they have multiplied, especially in certain 

 cases, so as to cover a greater area, as might at first be supposed. This 

 power of movement of the pigment cells, I believe, explains quite readily 

 the aggregation of these bodies in the vicinity of the parasitic cysts 

 found in the skin of the Cunner. That the distribution of the coloring 

 tissue has been motlified iu the si^ecimens before us no one can deny, 

 and I am loth to believe that the color-bearing cells have been multi- 

 plied in consequence of the irritation caused by the parasites. On the 

 lius, for example, wherever there is a cyst present, there the pigment is 

 sure to have accumulated, and in the light of our i)reseut knowledge I 

 see no more satisfiictory explanation of the fact than that here given. 



What stimulus other than irritation would be adequate to produce 

 the physiological impulse leading to the migration of the color-bearing 

 cells, I am quite unable to conceive. Can it be that the physiological 

 function of pigment cells is in this case defensive or reparative? It is 

 possible, in consequence of their nearness to the irritating cause, that 

 they are among the first amoeboid bodies on hand to attempt to assume 

 some protective function. That such is their function here I have also 

 no doubt whatever. If they are generated in consequence of the irrita- 

 tion produced by the parasite, which is very doubtful, then is there all 

 the more reason to suppose that they have a reparative or protective 

 function. Of one thing we may be sure, that they have some share 

 either directly or indirectly in carrying on some salutary metabolic pro- 

 cess, else we should not find them in the vicinity of the cysts, no matter 

 whether they are developed there de novo or have migrated into their 

 new i)ositions from adjacent groups of pigment cells which are, as is 

 well known already, very abundant in the skin of the Cunner. 



Washington, Novemler 7, 1883. 



