36 ON MAGNITUDE [ch. 



normal size ; and that these dwarf bodies were composed of only a 

 half, a quarter or an eighth of the normal number of cells. Similar 

 observations have been often repeated and amply confirmed. For 

 instance, in the development of Crefidula (a httle American 

 " shpper-hmpet," now much at home on our own oyster-beds), 

 Conkhn* has succeeded in rearing dwarf and giant individuals, 

 of which the latter may be as much as twenty-five times as big 

 as the former. But nevertheless, the individual cells, of skin, gut, 

 liver, muscle, and of all the other tissues, are just the same size 

 in one as in the other, — in dwarf and in giant f. Driesch has laid 

 particular stress upon this principle of a "fixed cell-size." 



We get an excellent, and more familiar illustration of the same 

 principle in comparing the large brain-cells or ganghon-cells, both 

 of the lower and of the higher animalsf . 



In Fig. 1 we have certain identical nerve-cells taken from 

 various mammals, from the mouse to the elephant, all represented 

 on the same scale of magnification ; and we see at once that they 

 are all of much the same order of magnitude. The nerve-cell of 

 the elephant is about twice that of the mouse in Unear dimensions, 

 and therefore about eight times greater in volume, or mass. But 

 making some allow^ance for difference of shape, the Unear dimen- 

 sions of the elephant are to those of the mouse in a ratio certainly 

 not less than one to fifty; from which it would follow that the 

 bulk of the larger animal is something like 125,000 times that of 

 the less. And it also follows, the size of the nerve-cells being 



* Conklin, E. G., Cell-size and nuclear-size, J. Exp. Zool. xii. pp. 1-98, 1912. 



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

 dogs ; Eabl, Z. f. w. Z. Lxvn, 1899. Cf. {i7it. al.) Pearson, On the Size of the Blood- 

 corpuscles in Rana, Biometrilca, 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 a hundred years before. But in this case, though the blood-corpuscles 

 show no relation of magnitude to the size of the animal, they do seem to have some 

 relation to its activity. At least the coipuscles in the sluggish Amphibia are much 

 the largest known to us, whQe the smallest are found among the deer and other 

 agile and speedy mammals. (Cf. Gulliver, P.Z.S. 1875, p. 474, etc.) This apparent 

 correlation may have its bearing on modem views of the surface-condensation 

 or adsorption of oxygen in the blood-corpuscles, a process which would be greatly 

 facilitated and intensified by the increase of surface due to their minuteness. 



% Cf. P. Enriques, La forma come funzione della grandezza: Ricerche sui 

 gangli nervosi degli Invertebrati, Arch. f. Entw. Mech. xxv, p. 655, 1907-8. 



