58 CELL-DIVISION AND GROWTH II. 2 



G. SMITH. Fauna und Flora des Golfes von Neapel : Rhizocephala, 

 Berlin, 1906. 



0. ZUR STRASSEN. Embryonalentwicklung des Ascarismegalocephala, 

 Arch. Ent. Mecli. iii, 1896. 



E. B. WILSON. Cleavage and mosaic work, Arch. Ent. Mech. iii, 1896. 



H. E. ZIEGLER. Ueber Furchung unter Pressung, Verh. Anat. GeseU. 

 viii, 1894. 



H. E. ZIEGLER. Untersuchungen uber die ersten Entwicklungsvor- 

 giinge der Nematoden, Zeilschr. Wiss. ZooL Ix, 1895. 



H. E. ZIEGLER. Experimented Studien iiber die Zelltheilung, Arch. 

 Ent. Mech. vii, 1898. 



2. GROWTH 



Following Davenport we define growth as increase in size or 

 volume. Since, therefore, growth is increase in all three 

 dimensions of space, it is most accurately measured not by 

 increase in some one dimension such as stature but by increase 

 of mass or weight. 



Growth depends upon the intake of food and the absorption 

 of water and exhibits itself in the form of increase in the amount 

 of living matter or of secretions of watery or other substances, 

 organic or inorganic, intra-cellular or extra-cellular, such as 

 chondrin, fat, mucin, cellulose, calcium phosphate, and the like. 



That growth depends in later stages at least upon the 

 intake of food is obvious. That it is due to the absorption of 

 water has been demonstrated effectively by Davenport for the 

 tadpoles of Amphibia (Amllystoma, liana, nfo). The method 

 employed was to weigh known numbers of the tadpoles at 

 different ages, desiccate and weigh again. The results of the 

 investigation are shown in the accompanying figure (Fig. 34), 

 from which it will be seen that the percentage of water rises with 

 remarkable rapidity from 56% to 96% during the first fortnight 

 after hatching. After that point the amount of water present 

 slightly but steadily declines. 



The same result is brought out by an analysis of the terminal 

 buds and successive internodes of plants. It is found in Iletero- 

 centron (Kraus) that the percentage of water rises rapidly from 

 the terminal bud to the first internode, more slowly from the 

 first to the second internode, and then remains constant. 



