[228] Bancroft, F. W., Jour. Exper. Zoöl., 1913, xv., 383.

[229] Loeb, J., Studies in General Physiology, Chicago, 1905, p. 2.

[230] Patten, Bradley M., Am. Jour. Physiol., 1915, xxxviii., 313.

[231] According to this theory the animal is not directly oriented by the outside force, e. g. the light, but selects among its random movements the one which is most “suited” and keeps on moving in this direc­tion. This idea is untenable for most if not all the cases of tropisms and has been refuted by practically all the workers in this field, e. g., Parker and his pupils, Bohn, H. B. Torrey, Holmes, Bancroft, Ewald, and others. It is only upheld by Jennings and Mast; and is accepted among those to whom the idea of a physico­chemical explana­tion of life phenomena does not appeal. Torrey and Bancroft (for the literature the reader is referred to Bancroft’s paper, Jour. Exper. Zoöl., 1913, xv., 383) have shown directly that the theory of trial and error is not even correct for the organism for which Jennings has developed this idea; namely Euglena.

[232] Loeb, J., and Maxwell, S. S., Arch. f. d. ges. Physiol., 1896, lxiii., 121.

[233] That the mechanisms by which helio­tropic and galvano­tropic orienta­tion is brought about are identical was shown by Bancroft in Euglena (Bancroft, loc. cit.).

[234] Loeb, J., and Maxwell, S. S., Arch. f. d. ges. Physiol., 1896, lxiii., 121.

[235] Loeb, J., Dynamics of Living Matter, p. 126.

[236] Loeb, J., and Maxwell, S. S., Univ. Cal. Pub., 1910, Physiol., iii., 195; Loeb and Wasteneys, Proc. Nat. Acad. Sc., 1915, i., 44; Science, 1915, xli., 328; Jour. Exper. Zoöl., 1915, xix., 23; 1916, xx., 217.

[237] Mast, S. O., Proc. Nat. Acad. Sc., 1915, i., 622.