OF THE SIZE OF CELLS 



61 



the leaf-cells are found to be of the same size in an ordinary water- 

 lily, in the great Victoria regia, and in the still hiiger leaf, nearly 

 3 metres long, of Euryale ferox in Japan*. Driesch has laid par- 

 ticular stress upon this principle of a "fixed cell-size," which has, 

 however, its own limitations and exceptions. Among these excep- 

 tions, or apparent exceptions, are the giant frond-like cell of a 

 Caulerpa or the great undivided plasmodium of a Myxomycete. 

 The flattening of the one and the branching of the other serve (or 

 help) to increase the ratio of surface to content, the nuclei tend to 

 multiply, and streaming currents keep the interior and exterior of 

 the mass in touch with one another. 



j^ 



Rabbit 



Man Dog 



Fig. 3. Motor ganglion-cells, from the cervical spinal cord. 

 From Minot, after Irving Hardesty. 



We get a good and even a famiUar illustration of the principle 

 of size-hmitation in comparing the brain-cells or ganghon-cells, 

 whether of the lower or of the higher animals f . In Fig. 3 we shew 

 certain identical nerve-cells from various mammals, from mouse to 

 elephant, all drawn to the same scale of magnification ; and we see 

 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 linear 



sluggish Amphibia are much the largest known to us, while the smallest are found 

 among the deer and other agile and speedy animals (cf. Gulliver, P.Z.S. 1875, 

 p. 474, etc.). This correlation is explained by the surface condensation or 

 adsorption of oxygen in the blood-corpuscles, a process greatly facilitated and 

 intensified by the increase of surface due to their minuteness. 



* Okada and Yomosuke, in Sci. Rep. Tohoku Univ. iii, pp. 271-278, 1928. 



t Cf. P. Enriques, La forma eome funzione della grandezza : Ricerche sui gangli 

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



