350 EDITH M. PRATT. 
As these cells are frequently observed in a partially- 
digested condition, they no doubt serve as a direct source of 
nutriment to the corals they inhabit. 
The zoochlorelle of the Aleyonaria are very similar to those 
described by Duerden (1903) in the Madreporaria, and do 
not apparently differ in any essential respect from those in- 
habiting other tropical corals. A cell usually has one, but many 
have two chromatophores. The presence of starch in these 
algal cells may be easily demonstrated by treating with a dilute 
solution of caustic potash followed by iodine solution. A starch 
ring, sometimes incomplete, is then seen to surround the pyre- 
noid, and in many cases starch grains are scattered about the 
middle of the cell. The presence of reserve food material in 
the form of starch in these algal cells indicates a super- 
abundance of nutriment. This insoluble food material can 
only be converted into a soluble form, such as sugar, by the 
action of diastase secreted by the protoplasm of the alga or 
possibly also by the animal cell which it inhabits. /It is 
well known to botanists that the vegetative cells of plants 
may convey nutriment in soluble form from one cell to 
another. In lichens nutriment of a carbohydrate, and possi- 
bly also of a nitrogenous nature is prepared by the algal cells 
and is conveyed to the symbiotic fungus through the walls of 
the algal cells and fungal hyphe. 
Zoochlorellz occur only in those portions of the corals which 
are exposed to lhght, and are most abundant in the endo- 
dermal cells and spaces, continually bathed with sea water, 
which circulates more or less freely within the colony through 
the zooids and canals. It is obvious that the circulating sea 
water rapidly becomes charged to a generous extent with 
carbon dioxide and other products of animal metabolism. 
The presence of carbon dioxide in considerable proportion 
would enable the rapid formation of carbohydrate food- 
material in the algal cell under the influence of sunlight. 
These cells have also the power to build up organic nitrogenous 
1 For information on the nutrition of vegetable cells I am indebted to 
Professor Weiss. 
