180 
ACTINIAD^. 
character of their skin. He treated them accordingly, and 
in a few days they assumed the usual plump condition. 
Facts seem to show that even the same individual is 
liable to considerable change of colour. Mr. Cocks tells 
me that from some hundreds of experiments he has ascer- 
tained that “ the colour is materially changed by diet, 
good or bad ; by water, pure or impure ; by attention or 
neglect; by over-feeding or starvation.” And Mr. E, L. 
Williams, jun. has favomred me with still more precise 
statements on this very species. He observes : — “ A. me- 
sembryanthemum does change. Bright green in two 
months has got to dark olive in my tank ; bright amber 
to dark brown ; brown with vertical yellow spots or dots 
has lost these markings.” 
Characteristic as are the marginal spherules, they are 
subject to some irregularities. I found a large specimen 
of the deep olive variety, which had on the exterior of the 
margin two azure tubercles; — one of them round, well 
defined, and in no respect distinguishable from the intra- 
marginal spherules, — the other somewhat less so. Below 
these, scattered down the side of the column, were four 
or five more blue warts ; more iiTegular in form and 
shape, but still well defined, and perfectly similar in their 
azure hue to the spherules. I subsequently obtained a 
second specimen with exactly the same peculiarities. On 
the other hand, a specimen of the same variety — which 
was sent me from Cumbrae by Mr. D. Eobertson about 
six months ago, and is still in my possession — has never 
showed the slightest trace of spherules, though in every 
other respect perfectly normal; the basal line and the 
gonidial tubercles being of the usual azure hue.* It is 
* “ M. Haime has remarked that these bourses ehromatophores, or 
calycine tubercles, are to the number of 18 in those individuals which 
have not yet developed the tentacles of the 5th cycle ; of 24 in those 
which have 6 or 5§ cycles, and of 48 in those which have 6 cycles com- 
