of Edinburgh, Session 1881-82. 
391 
2. For the yellow cells of Radiolarians and Ccelenterates he 
proposes the name Zooxanthella, to which I do not object, especially 
seeing that he so ably argued for their algal nature in his first 
paper. 
3. He observes that large Radiolarian colonies show no signs of 
digesting foreign bodies, that these and also Spongilla can be kept 
best in filtered water, and that the latter did not live in a half- 
darkened room. 
These statements are all doubtless true, but they constitute an 
extraordinarily slender foundation for the doctrine of “ symbio- 
sis.” Many Radiolarians can be easily observed to digest foreign 
bodies ; every sponge, whatever its colour, requires great quantities 
of thoroughly pure water to keep it alive, while of course every one 
who has worked with living Radiolarians must have felt the 
necessity of transferring them when he wished to prolong their 
life from the impure water of the “ Auftrieb,” teeming as it is with 
dead and dying Crustaceans, fragments of Siphonsphores, and all 
manner of other impurities, to pure water. I am not surprised 
that Dr. Brandt did not mention this trivial fact as evidence for 
the algal nature of the yellow cells in his first paper. 
4. Upon the above evidence , Dr. Brandt concludes that the algae 
maintain their hosts ; that so long as the animals contain few or 
none they feed in the ordinary way, but when sufficient algse are 
present, they are nourished like plants. This may perhaps be the 
case in Collozoum and some other Radiolarians, but Anthea, Velella , 
&c., are quite as voracious as their congeners unprovided with 
chlorophyll. He further indicates an analogy to lichens (an 
hypothesis which, as I also state above, was first ventured by 
Semper, and which can hardly fail to have suggested itself to 
every observer since Cienkowski), and points out a distinction, 
since in a lichen there is an association of an alga with a true 
parasite, here a “ symbiose ” of algae with animals accustomed to 
independent life, which they however give up, and take in no 
further nutriment. Thus “ in a morphological sense the algae, in 
a physiological sense the animals, are the parasites.” 
I have already (p. 380) given Dr. Brandt full credit for the valua- 
able observations contained in his first paper. So I should be 
extremely sorry to depreciate the theoretic insight of the present 
