V] OF FLAGELLATE CELLS 435 



pointed and flagellate cell of a Monad, one of the least and com- 

 monest of micro-organisms, is far removed from a simple "drop," 

 and all its characters, to the microscopist's eye, are both generally 

 and Specifically those of a hving thing. But a drop of water falhng 

 through an electric field, as in a thunderstorm, is found to lengthen 

 out to three or four times as long as it is broad; and then, if the 

 strength of the field increase a httle, the prolate drop becomes 

 unstable, it grows spindle-shaped, and suddenly from one of its two 

 pointed spindle-ends (the positive end especially) a long and slender 

 filament shoots out, to the accompaniment of an electrical discharge. 

 We need not assert that the phenomena are identical, nor that th^ 

 forces in action are absolutely the same. Yet it is no small thing to 

 have learned that the pecuhar conformation of the Httle flagellate 

 Monad has its analogue in an electrified drop, and is not unique after 

 all*. 



Before we pass from the subject of the conformation of the 

 solitary cell we must take some account of certain other exceptional 

 forms, less easy of explanation, and still less perfectly understood. 

 Such is the case, for instance, of the red blood-corpuscles of man 

 and other vertebrates; and among the sperm-cells of the decapod 

 Crustacea we find forms still more aberrant and not less perplexing. 

 These are among the comparatively few cells or cell-like structures 

 whose form seeins to be incapable of explanation by theories of 

 surface-tension. 



In all the mammalia (save a very few) the red blood-corpuscles 

 are flattened circular discs, dimpled in upon their two opposite sides. 

 This configuration closely resembles that of an india-rubber ball 

 when we pinch it tightly between finger and thumb •)". 



The form of the corpuscle is symmetrical ; it is a sohd of revolu- 

 tion, but its surface is not a surface of constant mean curvature. 

 From the surface-tension point of view, the blood-corpuscle is not 

 a surface of equilibrium ; in other words, it is not a fluid drop poised 



* Cf. W. A. Macky, On the deformation of water-drops in strong electric fields, 

 Proc. B.S. (A), cxxxiii, pp; 565-587, 1931. 



t On this analogy we might expect the double concavity to pass, with no great 

 difficulty, into the single hollow of a cup or bell, and such a shape the blood- 

 corpuscles are said sometimes to assume. Cf. Weidenreich, Arch. f. mikr. Anat. 

 Lxvii, 1902; and cf. Clerk-Maxwell on "dimples" in Tr. R.S.E. xxvi, p. 11, 1870. 



