538 Cf. pp. 255, 463, etc.

539 In a few cases, according to Awerinzew and Rhumbler, where the chambers are added on in concentric series, as in Orbitolites, we have the crystalline structure arranged radially in the radial walls but tangentially in the concentric ones: whereby we tend to obtain, on a minute scale, a system of orthogonal trajectories, comparable to that which we shall presently study in connection with the structure of bone. Cf. S. Awerinzew, Kalkschale der Rhizopoden, Z. f. w. Z. LXXIV, pp. 478〓490, 1903.

540 Rhumbler, L., Die Doppelschalen von Orbitolites und anderer Foraminiferen, etc., Arch. f. Protistenkunde, I, pp. 193〓296, 1902; and other papers. Also Die Foraminiferen der Planktonexpedition, I, 1911, pp. 50〓56.

541 Bûˋnard, H, Les tourbillons cellulaires, Ann. de Chimie (8), XXIV, 1901. Cf. also the pattern of cilia on an Infusorian, as figured by Bû¥tschli in Bronn〙s Protozoa, III, p. 1281, 1887.

542 A similar hexagonal pattern is obtained by the mutual repulsion of floating magnets in Mr R. W. Wood〙s experiments, Phil. Mag. XLVI, pp. 162〓164, 1898.