Coloration of Marine Animals. 233 
specially delights in the dark surfaces of stones in rock-pools 
from low-water mark to some distance above half-tide ? The 
unpractised eye would certainly mistake these rough little 
lumps for muddy and stunted masses of zoophytes and debris. 
How are their gem-like dots of pigment to be explained? 
Rarely Agirus has been found crawling just under the water- 
line in a sequestered pool. Polycera quadrilineata, P. ocellata, 
and Ancula cristata all occur under stones in quiet rock-pools, 
and are not difficult to detect in their habitats. It is doubtful 
if they are in want of protective or warning coloration in such 
places, especially when it is found that in these localities 
Doto coronata, which swarms on the branches of Sertularta 
pumila, requires careful and minute inspection to detect it. 
It is pale and devoid of much of the beauty of the deep- 
water specimens so often tossed on shore on the blades of the 
tangles covered by forests of Obelia geniculata or on Hydrall- 
mania falcata brought in by the fishing-boats. A clearer case 
of harmony with environment, however, is that of Z'ritonta 
plebeta on Alcyonium, yet it is readily seen when frequenting 
Obelia geniculata on the blades of tangles. 
On the other hand, the dog-whelk between tide-marks 1s 
fairly conspicuous, and so is the cowry, especially when the 
soft parts are protruded. ‘The colours of the Kolids are 
remarkably bright, and cannot therefore be protective in so 
far as being in harmony with their surroundings. It has 
yet to be proved that they are warning colours, for it needs a 
considerable amount of inedibility to scare a hungry fish, and 
the cod does not respect this property (if it exists) in Holis 
papillosa. Fishes which are partial to anemones might be 
supposed to be careless of the nematocysts of Nudibranchs. 
Further, the haunts of the Holides and an attentive survey 
of their coloration leads to no conclusive results. The 
amethystine and ultramarine hues of #. coronata and the 
scarlet or bright brick-red of EZ. rufibranchialis seem to have 
no relation to their surroundings, and does not prevent their 
being devoured by their hungry fellows when disabled or 
dead. ‘The same may be said of the fine purplish and the 
orange varieties of Holis Warrant and of EL. Adelaide, The 
smaller Hols olivacea and E. viridis are not so easily seen on 
the under surfaces of the stones they frequent ; but immersion 
of these in sea-water readily shows them. 
Prof. Herdman, who has given much attention to the 
colours of Nudibranchs, truly considers that “ the red-brown ” 
hues of Dendronotus effectively conceal it. Some, however, 
are brightly tinted with scarlet and rose-pink, and a splendid 
white variety is common in the same haunts in deep water 
