148 TBOPISMS 



by certain substances produced and excreted by the organ- 

 isms themselves, e.g., C0 2 . 



3. The results obtained with the spermatozoa of ferns 

 and mosses by Pfeffer and other botanists led some 

 authors to the tacit assumption that the spermatozoa of 

 animals were positively chemotropic toward substances 

 contained in or secreted by the eggs of the same species. 

 Some accepted this assumption without test, others made 

 tests which they considered adequate but which seem 

 doubtful, and it may be of some interest to discuss the 

 subject, since far-reaching conclusions might be based 

 on these experiments. Pfeffer's method of testing for 

 chemotropism with the aid of the capillary tube has proved 

 satisfactory and the application of this method has shown 

 that the spermatozoa of certain animals, e.g., of sea 

 urchins, are not chemotropic toward substances contained 

 in or given off by the egg. Thus Buller, who had worked 

 in Pfeffer's laboratory on the chemotropism of the sper- 

 matozoa of ferns, investigated carefully and extensively 

 the question whether or not the spermatozoa of echino- 

 derms are positively chemotropic for egg substances. 90 

 His results were entirely negative. Thoroughly washed, 

 ripe unfertilized eggs of Arbacia (Naples) were put into a 

 small volume of sea water for from 2 to 12 hours. 



Capillary glass tubes, about 12 mm. long and 0.1 to 0.3 mm. internal 

 diameter, and closed at one end, were then half filled with the (super- 

 natant) sea water (which had contained the eggs) by means of an air 

 pump. The tubes were then introduced into a large open drop of sea 

 water, in which fresh, highly motile spermatozoa were swimming. If 

 the eggs excrete an attracting substance it was argued that it should 

 be present in the tubes, and the spermatozoa should collect there. . . . 

 No attraction into the tube could be observed. Except for a surface- 

 contact phenomenon to be further discussed, they went in and out with 

 indifference. Apparently, therefore, the water which had contained the 

 eggs exercised no directive stimulus on the spermatozoa whatever. 



