60 ON MAGNITUDE [ch. 



or into a star; but ethereal pressure is an opponent force leading 

 to disruption, negligible on the small scale but potent on the large. 

 High up in the scale of magnitude, from about 10^^ to 10^^ grams 

 of matter, these two great cosmic forces balance one another; and 

 all the magnitudes of all the stars he within or hard by these narrow 

 limits. 



In the hving cell, Sachs pointed out (in 1895) that there is a 

 tendency for each nucleus to gather around itself a certain definite 

 amount of protoplasm*. Drieschf, a httle later, found it possible, 

 by artificial subdivision of the egg, to rear dwarf sea-urchin larvae, 

 one-half, one-quarter or even one-eighth of their usual size; which 

 dwarf larvae were composed of only a half, a quarter or an eighth 

 of the normal number of cells. These observations have been often 

 repeated and amply confirmed : and Loeb found the sea-urchin eggs 

 capable of reduction to a certain size, but no further. 



In the development of Crepidula (an American "shpper-Hmpet," 

 now much at home on our oyster-beds), ConklinJ has succeeded in 

 rearing dwarf and giant individuals, of which the latter may be 

 five-and-twenty times as big as the former. But the individual 

 cells, of skin, gut, liver, muscle and other tissues, are just the same 

 size in one as in the other, in dwarf and in giant §. In like manner 



* Physiologische Notizen (9), p. 425, 1895. Cf. Amelung, Flora, 1893; Stras- 

 biirger, Ueber die Wirkungssphare der Kerne und die Zellgrosse, Histol. Beitr. (5), 

 pp. 95-129, 1893; R. Hertwig, Ueber Korrelation von Zell- und Kerngrosse 

 (Kernplasraarelation), Biol. Centralbl. xvm, pp. 49-62, 108-119, 1903; G. Levi 

 and T. Terni, Le variazioni dell' indice plasmatico-nucleare durante 1' intercinesi, 

 Arch. Hal. di Anat. x, p. 545, 1911; also E. le Breton and G. Schaeffer, Variations 

 hiuchimiqiies du rapport nucleo-plasmatique, Strasburg, 1923. 



t Arch.f. Entw. Mech. iv, 1898, pp. 75, 247. 



X E. G. Conklin, Cell-size and nuclear size, Journ. Exp. Zool. xii, pp. 1-98, 

 1912; Body-size and cell-size, Journ. of Morphol. xxiii, pp. 159-188, 1912. Cf. 

 M. Popoff, Ueber die Zellgrosse, Arch.f. Zellforschung, iii, 1909. 



§ Thus the fibres of the crystalline lens are of the same size in large and small 

 dogs, Rabl, Z.f. w. Z. lxvii, 1899. Cf. {int. al.) Pearson, On the size of the blood- 

 corpuscles in Rana, Biometrika, vi, p. 403, 1909. Dr Thomas Young caught sight 

 of the phenomenon early in last century: "The solid particles of the blood do not 

 by any means vary in magnitude in the same ratio with the bulk of the animal," 

 Natural Philosophy, ed. 1845, p. 466; and Leeuwenhoek and Stephen Hales 

 were aware of it nearly two hundred years before. Leeuwenhoek indeed had 

 a very good idea of the size of a human blood-corpuscle, and was in the habit of 

 using its diameter — about 1/3000 of an inch — as a standard of comparison. But 

 though the blood-corpuscles shew no relation of magnitude to the size of the 

 animal, they are related without doubt to its activity; for the corpuscles in the 



