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one. I must, however, point out that the theory stated by Dr. 
Brandt of symbiosis between animals and algae is, by his own 
showing, founded upon two lines of argument, first, that relating to 
“ Zoochlorellaf which we have seen to be no alga at all, and 
secondly that from the very simple fact that captive Badiolarians 
live longer in pure water ! Such being the case, it is evident 
that (1) the demonstration of the truth of Cienkowski’s view that 
the yellow cells of Radiolarians and Ccelenterates are algae, (2) the 
development of Semper’ s hypothesis of the lichenoid nature of the 
alliance between alga and animal into a theory of mutual inter- 
dependence, and (3) the transference of that hypothesis from 
the region of plausible speculation into that of experimental science, 
remain with my paper. 
For it will not do to ignore, with Dr. Brandt, such weighty 
opposing evidence as (1) the recent direct statement of Hamann 
that the yellow cells of Medusae, &c., are not algae, but unicellular 
glands, (2) the observation of Krukenberg that Antliea cereus did 
not evolve oxygen in sunlight, or (3) the failure of himself and 
others to prove the presence of cellulose and chlorophyll, or even to 
confirm Haeckel’s discovery of starch in Badiolarians, observations 
which rendered the whole matter so utterly dubious that no 
botanist had ever accepted it, although its value, especially to 
disciples of Schwendener, is obviously great. But for the necessity 
of meeting these objections point by point, I might have published 
the doctrine of reciprocal accommodation before going to Naples at 
all. The temptation was strong, but then the subject would have 
remained as with Senrper and indeed also with Dr. Brandt, in the 
region of unproved hypothesis, instead of demonstrated fact.* 
Nor is the theory of complete reciprocal accommodation between 
plant and animal entitled to supersede the at first sight more 
natural view held by Cienkowski, and formerly also by Dr. Brandt, 
of simple parasitism of the yellow bodies, until it has been shown, 
(1) that animals containing algae are actually successful beyond 
* I must also point out with reference to Dr. Brandt’s latest republication 
( Archiv . /. Anat. u. Physiol., 1882, p. 125), that the identity of Hydra fusca 
and Hydra viridis was made known several years ago by Duplessis, and with 
respect to the plate, that his figures of green infusors and their chlorophyll 
grains have been anticipated by Claude Bernard, Lemons sur les Phenomenes de 
la Vie, kc., Paris, 1878. 
