UOLBLY-Sl'O'ITKI) (;()I5V. 



258 



spot, is adoi'ned with somiMvhnt imperfect, vertical stri- 

 pes of a varying cherry and yellow colour, which pos- 

 teriorly become fainter ajid finally disappear. On each 

 of the dorsal fins there are tlu-ee horizontal, deep cherry 

 stripes, separated by streaks wliicii apjjear now of a 

 deeper or fainter yellow, ii(n\- green. 



"The pupil has a strange, deep l)iiie lu.stre. The 

 iris is marked with foiu" copper-brown spots, set obli- 

 quely in a cross. 



'"In the female all these colours, especially the 

 markings of the dorsal fins and tlic iridescent sjjots on 

 the sides, are much fainter. 



"This description may fail to give more than a 

 feeble idea of the beauty of the fish at a given moment. 

 I say mome>if, for under certain circumstances almost all 

 tills brilliancy may nioi-e or less suddenly and com- 

 pletely vanish, or only lea\e traces behind to reappear 

 just as quickly. 



"On putting one of these small fishes, while still 

 alive, beneath the microscope, we see that several kinds 

 of variously-coloured chromatophores (pigment-cells) lie 

 scattered in the skin. In old specimens the black chro- 

 mntojjJiores are most numerous, occurring almost every- 

 where on the body, and tliickest on the back, at the 

 base of the caudal tin and Itehind the base of the pec- 

 toral tins, ^vhere tliey form the black spots already 

 mentioned, and along the base of the anal fin in the 

 males. The i/elloir or greenish-i/eUoir cliromato'phores 

 are more numerous than the black in young specimens, 

 but not so in old. They occur on every ])art of the 

 body, with the exception of the [sectoral and ventral 

 fins, and are especially prominent on the unpaired fins, 

 where they form the yellow and yellowish green streaks 

 already mentioned. When contracted, thej- are yello^vish 

 red. The orange or red rhromafophores are less nume- 

 rous than the preceding ones. They occur in small 

 numbers on the body and in greater number on the 

 head, but are most numei-ous on the unpaired fins, 

 where they form the cherry stripes mentioned above. 

 When contracted, their colour varies from reddish 

 brown to black. In the selliforni spots, on the top of 

 the head and on the belly ai'e collected chromatophores" 

 filled with small disks of a metallic lustre (glitter). In 

 their ordinary, expanded state they are confluent, form- 

 ing an unbroken network. Most of these chromato- 

 phores apparently contain black or yellow pigment in 



tiie middle; but perhaps these apparently central collec- 

 tions of pigment i-eally lie only on the outside of the 

 chromatophores — this question is not yet solved. 



"Tlie fish has the power of now contracting, and 

 now more or less expanding these different chromato- 

 phores in a myriad ways, thus causing tlic most varying 

 and unexpected arrangement of colours. Tliis alteration 

 in tlie degree of expansion of the chromatophores .seems 

 to proceed without a moment's pause, but unfortunately, 

 in consequence of the restlessness of the fisli while un- 

 der examination, can only very imperfectly be followed 

 bv the observer. The cells do not seem to be at per- 

 fect rest for a single instant; and the colour of the 

 fish undergoes incessant, more or less sudden, irregular 

 variations. 



"If, for example, Ave completely cover Avith a small 

 box a specimen taken during the spawning-season and 

 of bright coloration, and keep it thus concealed for two 

 or three minutes, or even only one, on removing the 

 box we find the fish entirely changed. There is now 

 not a trace left of the selliform spots; the whole of the 

 variegated dress has disappeared, and is replaced by a 

 monotonous shade of brownish black or blackish green. 

 But this dark colour changes visibly under the influ- 

 ence of light. We see how the selliform spots reappear 

 in their original places. The upper surface of the head 

 becomes lighter. The contrast betAveen the light colour 

 of the belly and the dark tint of the back increases. 

 After a minute or tAvo the fish is as variegated as be- 

 fore. If. on removing the box, Ave throAv a ray of 

 sunlight on the fish by means of a mirror, this altera- 

 tion takes place much more rapidly. 



"If, instead of covering the fish, Ave place it in 

 water Avith a black substratum, it also turns perfectly 

 dark, tliough only after an interval of some length. 

 The selliform spots again disappear almost entirely. 

 The black pectoral spots and the caudal spot scarcely- 

 stand out on the ground-colour. Only the belly re- 

 mains light, for there the black chromatophores are 

 Avanting. If the fish, together Avith the black substratum, 

 be noAv put under the microscope, all the black chro- 

 matophores are seen to be expanded to the uttermost. 

 Even the parts previously occupied by the selliforni 

 spots are noAv so closelv filled Avith these chromato- 

 phores, though here their number is small, that the 

 dull lustre can no lonjjer maintain its usual degree ot 



" Called iriciocytes by Pouchet. Cf. below, oi\ tlie variations of colour in the Flounders (p. 367). 



