62 SYMBIOGENESIS 



synthetic labour until eventually after a short period of 

 inflation a corresponding- degree of physiological and economic 

 sterility is reached. Finally, in other cases of similar decline 

 the further stage of utter physiological bankruptcy illustrated 

 by obligatory parasitism ensues in due course. 



The changes produced in the animal by this undue 

 " intimacy," this retrograde symbiosis, are no less startling 

 than those produced on the algae, for it has lost its excretory 

 system, which, surely, is not a progressive atrophy, but pure 

 degeneration. "Unlike their allies, such animals possess no 

 apparatus for the systematic discharge of the waste products 

 of their metabolism." 



What becomes of the waste products " compounds of 

 nitrogen of a kind useless to the animal " ? They are stored in 

 the tissues of the body, and Prof. Keeble informs us that, 

 though they are useless for the nutrition of the animal, they 

 serve well for plants. This last remark, however, should be 

 qualified by the addendum that though such substances may 

 serve for the nutrition of plants, yet they do so more or less 

 retrogressively. In Survival and Reproduction I have pointed 

 out that an excess of nitrogen produces injurious effects upon 

 plants, and that the notion so widely held that the effective- 

 ness of manure is proportionate to its unsavouriness is based on 

 fallacies. Plants, on the contrary, suffer in viability from 

 such manure which induces a " dyspeptic " condition of the 

 soil. 



The green and yellow-brown cells, then, in the bodies of 

 the Convoluta spoken of in this connection by Prof. Keeble 

 as the " hosts " obtain access to and utilise the stores of waste 

 nitrogen-compounds accumulated therein. 



The plants flourish in the bodies of these animals because there 

 they discover large accumulations of waste nitrogen compounds; the 

 animals, looking to the algae to come and take charge of the work of 

 getting rid of these waste substances, have ceased to construct any 

 excretory apparatus whatever. Hence it is not surprising that, when 

 the algse fail to appear in their bodies, the animals suffer. It may 

 be that the death of uninfected animals is not merely the consequence 



