DOUBLY-SPOTTED GOBY. 
spot, is adorned with somewhat imperfect, vertical stri- 
pes of a varying cherry and yellow colour, which pos- 
teriorly become fainter and finally disappear. On each 
of the dorsal fins there are three horizontal, deep cherry 
stripes, separated by streaks which appear now of a 
deeper or fainter yellow, now green. 
“The pupil has a strange, deep blue lustre. The 
iris is marked with four copper-brown spots, set obli- 
quely in a cross. 
"In the female all these colours, especially the 
markings of the dorsal fins and the iridescent spots 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 moment , for under certain circumstances almost all 
this brilliancy may more or less suddenly and com- 
pletely vanish, or only leave 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- 
matophores are most numerous, occurring almost every- 
where on the body, and thickest on the back, at the 
base of the caudal fin and behind the base of the pec- 
toral fins, where they form the black spots already 
mentioned, and along the base of the anal fin in the 
males. The yellow or greenish-yellow chromatophores 
are more numerous than the black in young specimens, 
but not so in old. They occur on every part of the 
body, with the exception of the pectoral and ventral 
fins, and are especially prominent on the unpaired fins, 
where they form the yellow and yellowish green streaks 
already mentioned. When contracted, they are yellowish 
red. The orange or red chromatophores 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 numerous on the unpaired fins, 
where they form the cherry stripes mentioned above. 
When contracted, their colour varies from reddish 
brown to black. In the selliform spots, on the top of 
the head and on the belly are 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 
25 3 
the middle; but perhaps these apparently central collec- 
tions of pigment really lie only on the outside of the 
chromatophores — this question is not yet solved. 
“The fish has the power of now contracting, and 
now more or less expanding these different chromato- 
phores in a myriad ways, thus causing the most varying 
and unexpected arrangement of colours. This alteration 
in the degree of expansion of the chromatophores seems 
to proceed without a moment’s pause, but unfortunately, 
in consequence of the restlessness of the fish while un- 
der examination, can only very imperfectly be followed 
by 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, we completely cover with 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 between the light colour 
of the belly and the dark tint of the back increases. 
After a minute or two the fish is as variegated as be- 
fore. If, on removing the box, we throw 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, we place it in 
water with a black substratum, it also turns perfectly 
dark, though 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 
wanting. If the fish, together with the black substratum, 
be now put under the microscope, all the black chro- 
matophores are seen to be expanded to the uttermost. 
Even the parts previously occupied by the selliform 
spots are now so closely filled with these chromato- 
phores, though here their number is small, that the 
dull lustre can no longer maintain its usual degree of 
Called iridocytes by Poucbet. Cf. below, on the variations of colour in the Flounders (p. 367). 
