XII 



place where the Oxytrichae turn. The triangles have 

 Hie same signification with regard to the Paramccia; 

 whereas the asterisks mark the whirling points 

 of the latter. The dotted line represents the 

 course of a Vorticella. It is easy to see that the 

 Parcimecia draw back even before they reach the 

 territory of the dead bodies; the Oxytrichae just 

 penetrate into it, both turning round at a certain 

 distance from the edge of the water drop in which 

 they swim, whereas the Vorticella advances to the 

 edge and even shirts it, without being influenced 

 by the presence of the dead bodies, 

 e. This insensibility seems to be peculiar to Vorticellae. 

 I have made analogous experiments on a great num- 

 ber of Ciliata of different species: they have all shown 

 the same necrophobia except two species of Vorti- 

 cella which remained totally insensible to dead 

 bodies of foreign species, as well as of their own, 

 and this to such a degree as to even touch the dead 

 bodies in passing. The ,,sessility" of the Vorticellae 

 may have something to do with this exceptional 

 quality, but at any rate we find this quality in the 

 Vorticellae whether they be fixed or free swimming 

 in the form of a campanula on its pedoncule or after 

 having taken the form of a barrel. 

 It is still impossible for me to give any exact infor- 

 mation concerning the substance or the substances 

 having this strong chemotactic action. 



The fact in question is perhaps not of great impor- 

 tance to general biology, but, no doubt, it is of interest 

 as it permits us, by means of an easy, simple and, at 

 the same time, most instructive experiment to show 



(1) a typical case of negative chemotaxis, 



(2) the great quantitative and qualitative differences 



