ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 243 



" (1) In carefully examining large colonies of Eadiolaria, I have 

 not found, either in their gelatinous matter or in its neighbourhood, 

 any foreign bodies which had undergone digestion. Inasmuch as they 

 require, by reason of their very considerable bulk, large quantities of 

 nourishment, and as they are absolutely destitute of any power of 

 manufacturing organic substances out of water, carbonic acid, and 

 ammonia, they cannot be kept alive by any other means than the 

 yellow cells which they harbour in large quantities. (2) I have been 

 able to keep the colonies with ease by placing them in well-filtered 

 sea-water : under these conditions they are deprived of all possibility 

 of nourishing themselves, like true animals, with solid organic 

 substances. (3) I have kept Spongilla in filtered river-water for the 

 same length of time. Even when the water has been filtered daily, 

 they have flourished wonderfully. But whenever the vessel was 

 placed in a half-darkened spot, they regularly died. Light is abso- 

 lutely necessary to them. 



" This proves, then, that Zooxanthella and Zoochlorella contribute to 

 the support of their hosts. As long as the animals contain but few or 

 no green or yellow cells, they are nourished like true animals, by the 

 absorption of solid organic materials ; as soon as they contain a 

 sufficient amount of algae, they are nourished like true plants, by 

 assimilation of inorganic materials. They ought to resume their 

 animal mode of nourishment when the algee withhold their functions, 

 in the absence of light. They perish if they do not then again adapt 

 themselves to the mode of alimentation which properly belongs to 

 them. 



" The researches of botanists have brought to light two different 

 ways in which algae may live in connection with other vegetable 

 organisms. Firstly, algae are found living like " lodgers " in other 

 chlorophyllaceous plants. Secondly, according to Schwendener, they 

 live in companionship with fungi, and with them form lichens. In 

 the first case the parasitic algse usually behave indifferently in relation 

 to the conditions of assimilation adopted by their hosts. The algas 

 are nourished like the plants in which they live, by assimilation of 

 organic matter. In the lichens, the algas furnish the nutritive matter 

 to the fungi, which live parasitically upon them. The algae manu- 

 facture organic substances out of inorganic substances, and the fungi 

 utilize them. 



" The association of algae and animals is an analogous case, but 

 nevertheless differs from it. In the green and yellow animals the 

 same phenomenon usually occurs ; the algae manufacture organic 

 substances from inorganic substances, and the animals make use 

 of them. But while in the lichens we find true parasites (fungi) 

 associated with algae, in the green and yellow animals we find 

 a symhiosis of algae with independent animals, habituated to an 

 independent existence. The animals (Phytozoa as they may be 

 termed) renounce their independent life and allow themselves to be 

 supported entirely by their parasites, when once the green or yellow 

 algae have entered their tissues and have multiplied there sufficiently. 

 They absorb no more solid organic substances, although they are 



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