THE CHARACTERISTICS OE ORGANISMS 17 



build up sugars, starch, and proteins, first of course for its own 

 maintenance and for its growth, thereafter for "reserves", variously 

 stored for its own future, or that of its offspring. On this 

 highly profitable synthesis and storage in the plant, the growth 

 of all animals depends — directly in the case of the sheep and 

 other herbivores, indirectly in the case of the tiger and other 

 carnivores. 



Food is thus obviously an indispensable condition of growth; 

 but there are some puzzling cases, e.g. the striking growth behaviour 

 of a single fragment of Planarian worm, without food-canal, and 

 thus incapable of ingesting food; yet soon growing a new head and 

 posterior end, fashioning itself anew into a perfect miniature worm. 

 Here, as in a germinating seed, there must have been absorption 

 of water and utilisation of the previous material in a less condensed 

 form. 



Another curious form of growth is expressed in the replacement 

 of lost parts, such as the claw of a crab, or the arm of a starfish; 



Fig. 3. 



Scale of Bony Fish, showing lines of growth (GrL) and the posterior teeth 

 (T). The portion to the convex side of the line LL is overlapped by 

 the scale in front — that is, nearer the head. 



and here again the body yields supplies. One of the most extra- 

 ordinary instances of such replacement-growth is that seen annually 

 when the stag, having dropped his antlers, rapidly grows a new 

 set, which, in the monarch, may weigh seventy pounds! 



The great majority of animals have a definite limit of growth, 

 an optimum size, which is normally attained by the adult and 

 rarely exceeded; so there must be some method of growth-regulation. 

 On the other hand, some fishes and reptiles continue growing as long 

 as they live, just like many trees; and this shows that a limit of 

 size is not fundamentally insisted on by nature. 



When we think of giants and dwarfs, and of the rarity of their 

 occurrence, the idea of regulation is again suggested. So also when 

 we observe the occurrence — yet rare occurrence — of monstrous 

 growths among animals, we see that growth is essentially a regulated 

 increase in the amoxmt of adjustment of living matter. By what 



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