THE DIGESTIVE ORGANS OF THE ALCYONARIA. 347 
smaller than in Lobophytum, and in some cases their pre- 
sence is extremely doubtful! They differ from those of 
Sarcophytumand Lobophytum in that they are frequently 
crowded with zoochlorelle, and from the latter genus also in 
that granular gland cells are very scantily distributed (fig. 
13, Scl. capitale). Fragments of zoochlorelle sometimes 
occur in the filaments, and there is little doubt that these 
cells are digested by the zooids. J have examined several 
specimens of the species of this genus, and have been unable 
to find other food material in the ccelentera, or in an ingested 
condition in the mesenterial filaments. The scarcity or com- 
plete absence of food material in the ccelentera of tropical 
corals is well known (p. 331), and has been commented upon 
by Hickson for Hydrocorallines, by Hickson, Bourne, 
Fowler, and Duerden for Madreporaria. Brandt and Hickson 
suggest that zoochlorelle contribute nutriment in a state of 
solution to the corals in a mature condition. 
After experimenting on Radiolaria and Anemones 
Famintzin (1891) maintains that these cells can only afford 
nutriment to the animals by the actual digestion of their tissues. 
Gamble and Keeble (1903) have experimented on Con- 
voluta roscoffensis, a Turbellarian which contains green 
cells in great abundance. They find that Convoluta feeds 
voraciously from the time of hatching to the period of 
maturity when it adopts a new mode of nutrition, and “ de- 
rives all its food directly from the green cells by digesting 
them, and possibly also indirectly by extricating plastic 
nutriment from them.” Dr. Gamble informs me that since 
the publication of this paper he has obtained evidence in 
favour of the last supposition. 
The foregoing comparative description of the histology of 
the genera Alcyonium, Lobophytum, and Sclerophy- 
tum indicates a reduction of the digestive surface 
of the autozooids in tropical forms associated 
1 In a specimen of Scl. Gardineri ventral mesenterial filaments were 
absent in many mature autozooids, but extremely small ones were observed 
in the case of young zooids. 
