352 THE STUDY OF ANIMAL LIFE CHAP. 



ultra-microscopic particles which were of the nature of 

 the chromatin which forms a great part of the nucleus 

 in all cells. He pictured them as specks of a substance 

 like chromatin, yet with definite specific individuality, 

 multiplying by binary fission, producing ferments, and 

 building up protein molecules. A later step was the 

 formation of an enveloping matrix of protoplasm and the 

 differentiation of a nucleus. The question of these be- 

 ginnings is wholly speculative, but the student should 

 recognise that there may have been many stages before 

 what we call a cell was evolved. 



Plants and Animals. One of the early steps must have 

 been the differentiation of two great lines of evolution - 

 the plant -line and the animal-line, whose resemblances 

 and differences have been already considered (chapter XI). 

 The cleavage depended on the production of the green 

 pigment chlorophyll, for it plays an indispensable part in 

 the " photosynthesis ' which is the most fundamental 

 process in animate nature. On the green plant's power 

 of utilising the energy of the sunlight in the upbuilding of 

 complex carbon- compounds from the raw materials of 

 water, earth, and air, the whole life of plants, and there- 

 fore of animals, depends. The bifurcation between 

 plants and animals may be regarded as expressing an 

 alternative of two possible regimes, between a life with 

 a relatively great preponderance of constructive, up- 

 building, synthetic processes (anabolism) and a life in 

 which there is a relatively large proportion of disruptive, 

 down-breaking processes (katabolism) an alternative 



which seems to have recurred frequently, in -less pro- 



A 

 nounced antithesis, in the history of organisms. If 



expressed the average vital ratio of anabolism to kata- 



o 



bolism in a plant and =- the same for an animal with the 

 same weight of living matter (if that could be estimated), 

 == is much greater than . - ; in other words, the animal 



JA. K 



lives much more nearly up to its income than the plant 

 does. 



