572 Bteller.—Contributions to our Knowledge of the 
direction of growth. Perhaps these useless reactions 1 are 
to be explained upon a theory of physiological correlation. 
The acquirement of one function may necessitate the acquire¬ 
ment of another The apparatus required for the reception 
interpretation and reaction in the case of one stimulus may 
be of such a nature that it may be set in motion by another 
stimulus. Thus the apparatus acquired for performing bio¬ 
logically useful movements by response to malic acid may 
be such in the case of the spermatozoa of Ferns that it can 
also be employed by rubidium chloride to give directive 
movements which have no biological advantage. 
II. The Withdrawal of Water from Spermatozoa. 
When a certain amount of water is withdrawn from sperma¬ 
tozoa they come to rest entirely. If after having been 
brought to rest in this way the spermatozoa are again allowed 
to absorb water freely, resumption of movement may take 
place. Similar facts have been observed for Bacteria 2 and 
other organisms. 
When a spermatozoon enters a capillary tube which con¬ 
tains a concentrated solution of a neutral salt, e. g. 5 gm % 
potassium nitrate, it moves slower and slower until, upon 
penetrating a certain distance into the tube, it ceases to move 
forward. The cilia, however, continue to move for some time, 
finally coming to rest. If the spermatozoon is carried out 
of the tube by the out-going under-current (see p. 556) the 
cilia recommence their motion. As less and less concentrated 
diffusion zones are reached the cilia move more and more 
rapidly. The spermatozoon soon begins to move slowly 
forward, the progression being in almost a straight line 
usually away from the mouth of the tube. Having arrived 
in the normal medium the organism moves more rapidly, but 
1 Useless reactions are also admitted by Goebel, Ueber Studium und Auffassung 
der Anpassungserscheinungen bei Pflanzen, Festrede, Akad. d. Wiss., Munchen, 
1898, p. 15. 
2 A. Fischer among others. Untersuchungen iiber Bacterien, Jahrb. f. wiss. 
Bot., 1895, p. 75. 
