48 SYMB10GENES1S 



It is a fact that C. roscoffensis, which is more moderate 

 and more symbiotic in its behaviour than C. paradoxa, is pre- 

 eminently gregarious and, by comparison, a slow breeder. 



C. paradoxa, which is less regular in its habits, less 

 reliant upon symbiosis than C. roscoffensis, and likewise less 

 abstemious, is solitary. Its large and surfeited eggs hatch with 

 extraordinary rapidity. 



During the very important period of maturing its eggs, 

 C. roscoffensis, as Prof. Keeble has shown, remains above all 

 temptation to devour anything, though the choicest bits may 

 be offered it. This is not the case with C. paradoxa, with its 

 gluttonous and surfeiting habits. It is a glutton throughout 

 its life, as Prof. Keeble has told us. Here, the bad habits have 

 become overpowering and such is the nemesis of bad specific 

 habits a corresponding surfeit of embryonic nutrition has to 

 be provided. I have dwelt on the importance of this explana- 

 tion of "reproductive nemesis " in previous volumes. 



The example of C. roscoffensis shows that the true need of 

 an animal is plant-food in due season and obtained under 

 conditions of symbiosis. The higher the degree of symbiosis 

 the higher the adequacy of the food and the resulting possi- 

 bilities for achieving rise of type. 



We are told by Pr*of. Keeble that green and yellow or 

 brown cells resembling in a general way those contained in 

 the bodies of C. roscoffensis and C. paradoxa are found in many 

 different kinds of animals belonging to the lower groups, and 

 further that, although sometimes there may be indications of a 

 former free living existence of the green cells, the case by no 

 means always stands so clearly. 



Indeed, the problems presented by the chlorophyllous cells of animals 

 are too numerous and important to be dismissed by means of a loosely- 

 drawn inference of this sort. To the possession of chlorophyll the plant 

 owes its powers of photosynthetic manufacture ; and to the absence of 

 this pigment from the cells of animals is due the dependence of the 

 animal world on the world of plants for food supplies. Yet, low down 

 in the animal kingdom, organisms exist which, though undoubtedly 

 possessed of distinct animal characteristics, contain chlorophyll and use 



