156 



DYNAMICS OF LIVING MATTER 



reverse behavior. The former organisms I designated as positively, 

 the latter as negatively, stereotropic. 



The first discovery in this direction was made by J. Dewitz,* who 

 found that the spermatozoa of the cockroach (Periplaneta orientalis) 

 are "attracted by surfaces." "If small pieces of glass or some other 

 object are placed between a shde and a cover-glass so that there is a 

 space between cover glass and shde, and if this space be filled with a 

 NaCl solution containing the spermatozoa, the latter gather only at 

 the cover glass and the slide. In the rest of the liquid no spermatozoa 

 are found. If a glass bead be put into such a liquid containing sper- 

 matozoa, the latter in no case leave the surface of the bead, although 

 they are constantly in motion." Dewitz recognized that this reaction 

 was of the greatest importance for the entrance of the spermatozoa 

 into the egg of the cockroach. This egg possesses a micropyle, and 

 only here can the spermatozoa enter the egg. When the egg is laid it 

 passes the duct of the seminal receptacle, where the female carries the 

 sperm it receives in the act of pairing. The egg then comes in contact 

 with the sperm, some of which is possibly pressed out of the receptacle 

 reflexly by the passing of the egg. When once on the surface of the 

 egg, the spermatozoa can no more leave it, but must move on its sur- 

 face incessantly. In this way one spermatozoon finally reaches the 

 micropyle and gets into the egg. The impregnation of the egg is there- 

 fore in this case a function of the stereotropism of the spermatozoa. 



Although stereo- 

 tropism is no real 

 tropism, inasmuch as 

 in this case lines of 

 force do not exist, there 

 exist stereotropic curva- 

 tures. When the stems 

 of Tuhularia are fixed 

 in an aquarium in such 

 a way that the polyp 

 touches the wall of the 

 aquarium (Fig. 34), 

 the polyp begins to 

 bend away from the 

 wall until at right 

 angles with it, and then continues to grow in this direction. The 

 stolon, however, sticks to the glass wall, possibly by the secretion of 

 a sticky substance. 



♦ J. Dewitz, PflUger's Arehiv, Vol. 37, p. 219, 1885; and Vol. 38, p. 358, 1886. 



Fig. 34. 



