Physiology of the Spermatozoa of Ferns. 547 
considerable light upon the manner in which the Ciliata and 
Flagellata respond to chemotactic stimuli. It appears that 
many of these organisms have a set of reflex movements 
which can be started by a variety of stimuli such as contact, 
heat or cold, certain salt solutions, acids, &c. Although no 
attention is paid to the position of objects and heat-centres, 
or to the direction of diffusion of dissolved substances setting 
up the reflex actions, the nature of the latter is such that the 
organisms move away from the source of stimulation. The 
same set of reflex actions is also able to cause an c attraction * 
toward solutions, &c. Such an ‘ attraction ’ is, however, only 
a particular case of a repulsion. While the majority of organ¬ 
isms investigated by Jennings appear to be chemotactic in 
the above manner, some were found apparently insensible to 
chemotactic stimuli. It is certain that in chemotropism the 
organisms concerned seek to grow along diffusion-lines. The 
existence of free-swimming organisms which are chemotactic 
in the sense that they move (directly or screw-wise) along 
diffusion-lines, although sufficiently probable, is not at present 
definitely known. 
Among the many interesting results of Pfeffer’s researches 
was the discovery 1 that the spermatozoa of the Ferns are 
strongly attracted by malic acid and its salts. A solution of 
o*ooi gm per cent, is sufficient to cause a chemotactic reaction. 
A large number of other substances 2 were tried but only the 
nearly related maleic acid 3 (as a sodium salt) was found to 
attract, while attraction by sodiummonobromsuccinate 4 re¬ 
mained doubtful. All the other substances tested, including 
those most widely found in plant-cells appeared to exert no 
attractive stimulus whatever. The possibility 5 of the dis¬ 
covery of other substances which attract was, however, ad- 
(4) Laws of chemotaxis in Paramecium, Amer. Journ. of Physiology, May, 
i 899 > P- 355 - 
(5) On the movements and motor reflexes of the Flagellata and Ciliata, 
Amer. Journ. of Physiology, vol. iii, Jan. 1900, p. 229. 
1 Pfeffer, loc. cit, Bd. i. 3 Loc. cit., Bd. i, pp. 411-13. 
3 Loc. cit., Bd. i, p. 382. 1 Loc. cit., Bd. ii, p. 655. 
5 Loc. cit., Bd. i, p. 412. 
