Ill] OF PARTS OR ORGANS 191 



results from it in the bodily form of the child and the man is easy 

 to see. 



The following table shews the relative sizes of certain parts and 

 organs of a young trout during its most rapid development; and 

 so illustrates in a simple way the varying growth-rates in different 

 parts of the body*. It would not be difficult, from a picture of the 

 little trout at any one of these stages, to draw its approximate 

 form at any other by the help of the numerical data here set 

 forth. In like manner a herring's head and tail grow longer, 

 the parts betw^een grow relatively less, and the fins change their 

 places a httle; the same changes take place with their specific 

 differences in related fishes, and herring, sprat and pilchard 

 owe their specific characters to their rates of growth or modes of 

 increment f. 



Trout (Salmo fario) ; proportionate growth of various organs 

 (From Jenkinson's data) 



Sachs studied the same phenomenon in plants, after a method 

 in use by Stephen Hales a hundred and fifty years before. On the 

 growing root of a bean ten narrow zones were marked off, starting 

 from the apex, each zone a millimetre long. After twenty-four 

 hours' growth (at a given temperature) the whole ten zones had 

 grown from 10 to 33 mm., but the several zones had grown very 

 unequally, as shewn in the annexed table J (p. 192): 



* Cf. J. W. Jenkinson, Growth, variability "and correlation in young trout, Bio- 

 metrika, vin, pp. 444-466. 1912. 



I Cf. E. Ford, On the transition from larval to adolescent herring, Journ. Mar. 

 Biol. Assoc. XVI, p. 723; xviii, p. 977, 1930-31. 8o also in larval eels, tail and 

 body grow at different rates, which rates differ in different species; cf. Johannes 

 Schmidt, Meddel. Kommlss. Havsiindersok. 1916; L. Bertin, Bull. Zool. France, 

 1926, p. 327. 



I From Sachs's Textbook of Botany, 1882, p. 820. 



