3] 



THIGMOTAXIS 



107 



orientalis. When an 0.8% or 0.9% NaCl solution contain- 

 ing spermatozoa was put under a cover-glass, the spermatozoa 

 arranged themselves in two layers, one in contact with the 

 cover-glass, the other in contact with the slide. By isolating 

 some of the spermatozoa at the upper surface and putting them 

 under a cover-glass, he found that they likewise distributed 

 themselves at both upper and lower surfaces. Hence the segre- 

 gation into two layers was not due to a difference in kind 

 between the spermatozoa occupying the two positions, but to 

 the fact that there were here two surfaces of contact, separated 



FIG. 20. A, Oxytricha seen from below; B, from the side; C, crawling over the 

 egg of Anodonta. (From VERWOBN, '95.) 



by a water-film. If a spherical grain be placed in the drop of 

 water, aggregation takes place about that also. A similar 

 experiment, with similar results, was made by MASSAET ("88) 

 with frog spermatozoa. Here, too, the active spermatozoa kept 

 in contact with the upper and lower glass surfaces, whilst the 

 weak forms lay midway between. The fact that only active 

 spermatozoa show this tendency to keep in contact with solids, 

 indicates that we are here dealing with irritability to contact. 



The quality of the surface influences its capacity for stimu- 

 lating to positive thigmotaxis. Thus, while mere roughness 

 has no effect, if the surface of glass be smeared with a slimy 

 mass, so thick that the spermatozoa can hardly penetrate it, 



