106 MOLAR AGENTS AND PROTOPLASM [Cn. IV 



pseudopod gradually extends itself, and new ones are formed, 

 until at last the whole substance of the amosba is spread out 

 parallel to the glass, over whose surface it moves. That there 

 is a considerable adherence is shown by the fact that the 

 amoeba is not disturbed by an appreciable current. If, how- 

 ever, it is made to contract, it looses its hold at once. 



Very similar phenomena occur, according to VERWORN ('95, 

 p. 429), in Orbitolites also. Such an organism lying in a watch 

 glass begins to send out pseudopodia which, so long as they 

 move free in the water, are simple straight threads ; but when 

 they touch the glass they adhere to it, stream out along it, and 

 send out branches. In these Rhizopoda, consequently, the 

 presence of a solid body is a stimulus to the spreading out of 

 the pseudopodia and to those changes by which close adhesion 

 is effected. 



We now pass to the other simple organisms. Among Infu- 

 soria, PFEFFER ('88, pp. 618-621) has found that Glaucoma 

 scintillans and, to a less degree, Colpidium colpoda, Parame- 

 cium aurelia, and Stylonychia mytilus aggregate about solid 

 bodies in the water, such as fragments of soaked filter paper 

 or particles of barium sulphate. Since these cannot supply 

 oxygen or soluble substances, the effect produced is doubtless 

 due to contact. 



The aggregated organisms tend, in moving, to keep upon the 

 surface of the solid. Thus PFEFFER ('88, p. 619) found that 

 Urostyla weissii, coming in contact with glass threads, moved 

 along them on their ventral surfaces ; and MASSART ('91) 

 observed some Chlamydomonades remain hanging to objects 

 with which they came in contact. VERWORN ('95, p. 431), 

 likewise, finds that Oxytricha travels over the surface of Ano- 

 donta eggs or particles of detritus which it happens upon in 

 the water. In one instance, the organism ran for some time 

 over the surface of an egg of Anodonta without being able to 

 leave it. After four hours, it was able, by the aid of a piece 

 of slime which came in contact with the egg, to free itself from 

 that body. 



Phenomena similar to the above-described for bacteria and 

 Infusoria are found in spermatozoa also. DEWITZ ('85 and 

 '86) first noticed this in the case of the cockroach, Periplaneta 



