442 



GENERAL PHYSIOLOGY 



are best known in the creeping plants and climbers, whose tendrils 

 and twining shoots turn toward the objects which they touch 

 and grow in constant contact with them (Fig. 218). Here the 

 structural relations are so complex that the behaviour of the living 

 substance within the single cellulose-capsule cannot be directly 



observed ; hence, thus 

 far it is not known with 

 certainty in what way 

 the individual cell shares 

 in the thigmotactic 

 twining. 



Dewitz ('86) found 

 positive thigmotaxis in 

 the spermatozoa of the 

 cockroach (Periplaneta 

 orientalis). If the sper- 

 matozoa be brought into 

 a 0*6 per cent, solution 

 of common salt between 

 the slide and the cover- 

 glass, after a short time 

 all the individuals collect 

 partly upon the lower 

 surface of the cover-glass, 

 and partly on the upper 

 surface of the slide, and 

 in these places describe 

 circles with their flagella, 

 the direction of which, 

 without exception, is op- 

 posite to that of the 

 hands of a watch. The 

 greater portion of the 

 liquid remains com- 

 pletely free from sper- 

 matozoa, the latter not 

 leaving the surface of the glass after having once reached it. 

 If a ball be placed in the drop, its surface is at once sought by 

 them. If a solution of common salt, containing spermatozoa, be 

 placed in the cavity of a ball, after a short time the whole inner 

 surface of the latter is covered, and the liquid in the middle is 

 completely deserted. The pronounced thigmotaxis of these sper- 

 matozoa, like the positive chemotaxis of many others, is of the 

 greatest importance for the fertilisation of the ova. 



A contrast to this behaviour of the spermatozoa of Periplaneta 

 is afforded by the following observation upon a genus of ciliate 

 Infusoria, Oxytricha. Their flat, yielding bodies are beset upon 



FIG. 217. Cyphoderia, with extended pseudopodia, stimu- 

 lated at ^ > . The protoplasm is flowing away 

 from the place of stimulation. 



