348 EDITH M. PRATT. 
with a corresponding increase in number of zoo- 
chlorelle,! and may be summarised as follows : 
1. The ventral mesenterial filaments of Lobophytum 
more closely resemble those of the British Aleyonium, and 
are only slightly reduced. Food material has beer observed in 
the coelentera of this genus. Zoochlorelle are never numerous. 
2. In Sarcophytum the mesenteries are modified by 
mesogloeal thickening near the free edge, but the filaments 
are smaller than those of Lobophytum, and are provided 
with few gland cells. Zoochlorelle are fairly numerous. 
3. The filaments of the tropical species of Alcyonium 
are extremely small, and contain few gland cells. Food 
material was not observed. Zoochlorellz are very numerous. 
4, The ventral mesenterial filaments in Sclerophytum are 
either very small or entirely absent.” When present, gland 
cells are so few in number that their physiological function 
must be extremely limited (fig. 13). No foreign food 
material was observed. Zoochlorelle are extremely numerous. 
From the comparatively small number of zooids in Sclero- 
phytum and the minute size of the tentacles it is obvious 
that the amount of food captured by the latter must be ex- 
tremely small and totally inadequate to supply the growing 
needs of a colony. Furthermore the minute mesenterial fila- 
ments—(the degenerate representatives of the principal 
organs of digestion in the British Aleyonium)—and the 
stomodzum are together incapable of digesting a sufficient 
amount of food to serve for the nutrition of an entire colony. 
I have already experimentally shown (p.332) that the natural 
food of the British Alcyonium appears to consist chiefly of 
small living crustacea, which, captured by the long and ex- 
tremely contractile tentacles, are paralysed by the poisoned 
threads of innumerable nematocysts before being swallowed. 
The absence of food in many tropical Alcyonaria may be 
1 A short account of the zoochlorelle in Aleyonaria, their nutritive 
function and geographical distribution is appended, p. 349. 
Ashworth (1898) states that Xenia Hicksoni from North Celebes 
has no mesenterial filaments. 
