Papers from the Department of Marine Biology. 
SUMMARY. 
The object of this paper is to point out that of the large number of 
species belonging to many phyla which habitually shelter amongst the 
branches of the crinoids of tropical reefs, by far the greater proportion 
exhibit colour resemblance to the host. As the colour scheme of the 
host is often extremely variable (e. g., Comanthus annulatum), that of 
the commensal, in some cases at least, varies too, but some commensals 
seem to be restricted in their response to the stimulus which causes this 
colour resemblance. Thus among the Crustacea, in Synalpheus all 
stages of variation are met with, according to the individual inhabited, 
between a pale form with very narrow stripes of pigment, to an extreme 
form totally covered with dark pigment; while in Cirolana, on the 
other hand, the individuals associated with even the darkest crinoids 
possess only insignificant lines of pigment on the otherwise totally 
white body. In the latter case there is, then, no protective resem- 
blance, although we witness the incipient stages of its establishment. 
Other forms like the polychet, the amphipod, and the brittle-star, 
Ophiomaza, give rise to dark varieties only and occur upon dark-green 
crinoids. 
The following represents in a tabular form the results of the obser- 
vations: 
Commensal. Pigments developed. Host and colour variety of host. 
All colour varieties of Coman- 
thus annulatum and some 
other crinoids. 
Comatula purpurea. 
Synalpheus brucei... .....200-- Purple-black 
Synalpheus brucet............. 
WS eo COMLALULATUINE.. - «pies aoe 
Curolana lineata... 0... sc5. nen 
Cyclotelson purpureum 
Pontoniopsis comanthi......... 
Periclimenes spp... ........5..- 
Ophiomaza cacaotica............ 
Ophiomaza cacaotica var. picta... 
Ophiomaza obscura............ 
POUR OG TUE pete a eis +. = 200s 6 
Brownish purple, purple 
and white. 
Red or purple in faint | 
thin lines, rest white. 
PAN OUT IE. cies, wets 2 .eus) snes 
Bright green and black or 
yellow and red-brown. 
Red and blue-purple..... 
Dark purple, brown or 
black. 
Black and white........ 
Dark brown and dull 
yellow. 
Dark brown or black..... 
All colour varieties of Coman- 
thus annulatum and some 
other crinoids. 
All colour varieties of Coman- 
thus annulatum and some 
other crinoids. 
Dark varieties of C. annulatum. 
Light (green or yellow) vari- 
eties of C. annulatum. 
Dark varieties of C. annulatum. 
Dark varieties of C. annulatum 
(one exception). 
Dark varieties of C. annulatum. 
Dark varieties of C. annulatum. 
Dark varieties of C. annulatum. 
