534 R. A. SPAETH 



This peculiarly inert behavior of the melanophores suggested 

 an inhibitory or even a toxic effect of the sea-water upon them. 

 Scales were consequently subjected to the action of distilled 

 water. A very definite reaction followed which has proved to 

 be entirely constant. 



When scales, taken from a light female, are immersed in dis- 

 tilled water at room temperature (20°C.), a rapid expansion of the 

 pigment is seen. As in the case of sea-water this occurs simul- 

 teneously in all the melanophores. The expansion continues for 

 some time — differing with the individual and depending also 

 upon the temperature of the distilled water and the size of the 

 scale. After a longer or shorter period of expansion a complete 

 contraction of all the melanophores follows. This contraction 

 invariably begins at the periphery of the scale and generally at 

 its posterior end (relative to the original position on the body of 

 the fish). Thence it creeps in towards the centre of the scale 

 much like the closing of an iris diaphragm. The melanophores 

 at the center of the scale often continue to expand for some time 

 after those at the periphery have begun to contract. Indeed, 

 individual melanophores lying in the region separating the ex- 

 panded from the advancing contracted phase frequently show 

 the pigment to be migrating proximally on the peripheral side 

 of the melanophore while on the inner side it continues to move 

 distally. Thus within the limits of a single melanophore the 

 pigment may, for a short time, be migrating reciprocally (figs. 

 1 to 5, pi. 1). 



The contraction which follows the first expansion in distilled 

 water is not, however, the final condition. After another time 

 interval (depending upon the factors previously mentioned), the 

 melanophores relax from the spheriform phase, the pigment ex- 

 tends a short distance out into the processes of the cells (never a 

 complete expansion) and from this semi-expanded state the mel- 

 anophores rapidly degenerate. This relaxation of the melano- 

 phores thus marks the approaching degeneration. 



When the melanophores, contracted in distilled water, are 

 examined with an immersion lens, they show the empty processes 

 of the cell from which the pigment has withdrawn to the center 



