192 J. EK. Durrpen—Jamaican Actiniaria : 
noticed that where the former are present in excessive amount, the latter are 
absent, and vice versa; the two may, however, exist side by side in the same 
species. ‘The granules are recognized as very small spheroidal bodies of various 
sizes, devoid of a nucleus and cell-wall, these being easily detected in the com- 
mensal algee. 
Most of the tissues of P. Swift are densely loaded with bright yellow granules 
of all sizes, but no zooxanthelle occur. The endoderm of P. dichroicus is also 
stated to be richly pigmented, and no zooxanthelle are seen. The converse holds 
in P. tunicans, the endoderm cells throughout contain an abundance of unicellular 
alge, but pigment granules are practically absent; P. monostichus and P. separa- 
tus show an admixture of granules and zooxanthelle. In the latter species a 
peculiar accumulation of brown pigment granules is found in the endoderm, about 
midway along the width of the mesenteries, this being the only occurrence in the 
polyp. 
Similar relationships of granules and zooxanthelle are afforded by other 
families of Actiniaria. According to my observations pigment granules only are 
present in Bunodes granulifera and B. Krebsii, while they are replaced by zooxan- 
thella: in Awlactinia stelloides. Most Sagartide contain zooxanthelle, but in 
Sagartia nivea (Verrill), the substitution of granules has occurred. The latter 
condition is also the case in Actinoporus elegans and in Corynactis myrcia already 
referred to. 
It seems likely that in some cases the pigment granules may perform the same 
function as the commensal algze—that of respiration. If this be so, we may per- 
haps regard them as free chromo-plasts, aggregated in the other case within distinct 
cells, the zooxanthelle. 
Although the amount and relative proportion of the inclusions vary, yet a 
curious similarity in their nature holds throughout the genus. Fine sand-grains 
and siliceous sponge spicules, with an occasional Radiolarian and Foraminiferal 
test, are characteristic of each species. Carlgren found much the same in 
Gerardia. . 
Haddon and Shackleton note the inclusions to be fairly numerous in P. angui- 
comus, and less so in P. axinelle and P. dizoni. Calcareous sand-grains predomi- 
nate in P. tunicans, and sponge spicules in P. monostichus, while both are numerous 
in P. separatus. In the two latter the majority of the spicules are similar to those 
of the sponge with which the anemone is commensal. 
A certain selection in the disposition of the foreign inclusions is also observable. 
Practically all the calcareous sand-grains of P. tunicans are limited to a narrow 
zone around the boundary of the ectoderm and mesoglcea ; while the sponge spicules 
are distributed throughout the middle layer, extending even to its inner boundary 
(Pls. xu. and xtv., fig. 4). Further, the spicules are most numerous in the capitular 
