275 BeitrûÊge z. Physiologie d. Protoplasma, Pflû¥gerãs Archiv, II, p. 307, 1869.
276 Poggend. Annalen, XCIV, pp. 447ã459, 1855. Cf. Strethill Wright, Phil. Mag. Feb. 1860.
277 Haycraft and Carlier pointed out (Proc. R.S.E. XV, pp. 220ã224, 1888) that the amoeboid movements of a white blood-corpuscle are only manifested when the corpuscle is in contact with some solid substance: while floating freely in the plasma or serum of the blood, these corpuscles are spherical, that is to say they are at rest and in equiôÙlibôÙrium. The same fact has recently been recorded anew by Ledingham (On Phagocytosis from an adsorptive point of view, Journ. of Hygiene, XII, p. 324, 1912). On the emission of pseudopodia as brought about by changes in surface tension, see also (int. al.) Jensen, Ueber den Geotropismus niederer Organismen, Pflû¥gerãs Archiv, LIII, 1893. Jensen remarks that in Orbitolites, the pseudopodia issuing through the pores of the shell first float freely, then as they grow longer bend over till they touch the ground, whereupon they begin to display amoeboid and streaming motions. Verworn indicates (Allg. Physiol. 1895, p. 429), and Davenport says (Experim. Morphology, II, p. 376) that ãthis persistent clinging to the substratum is a ãthigmotropicã reaction, and one which belongs clearly to the category of ãresponse.ããã (Cf. Pû¥tter, Thigmotaxis bei Protisten, A. f. Physiol. 1900, Suppl. p.
247.) But it is not clear to my mind that to account for this simple phenomenon we need invoke other factors than gravity and surface-action.