492 Dr. A. Gruber on the 



uniform, and the two animals glide quietly through sand- 

 grains, filaments of algge, &c., one after the other. But if the 

 anterior one meets with an obstacle, stops and swims back- 

 wards, the posterior Infusorian does this also at the same 

 time. It is therefore not as if the second individual simply- 

 followed the first, and if the first can go no further the second 

 would still endeavour for a time to swim forward until it is 

 held back. If one of the halves shrinks together in conse- 

 quence of an unpleasant contact, the other does so also at the 

 same moment ; in short all the movements are perfectly syn- 

 ctn-onous until the last uniting threadlet is ruptured between 

 the two individuals, each of which then swims away in a 

 different direction. The same result is obtained if we succeed 

 in making a transverse incision in a Stentor in such a manner 

 as to produce two halves, which, as in spontaneous division, 

 are united by a narrow bridge of protoplasm (fig. 15). Then 

 also these two loosely connected pieces move quite uniformly, 

 and one of them does not attempt to swim backwards while 

 the other steers forwards. As in this case the posterior half 

 lacks the peristome, the simultaneous movements are performed 

 by the body-cilia. If then, as these observations show, a 

 very slender and even thread-like bridge of protoplasm suffices 

 to cause the loosely connected pieces to behave as one physio- 

 lo"-ical individual, this proves that the nervous fanctions in 

 the Infusorial body are not confined to definite courses, and that 

 the exertion of loill uniformly governs every protoplasm-element. 

 Consequently no circumscribed central organ can be present ; 

 but every plasmatic particle is a central organ and conductor 

 in one, i. e. the nervous potency of the cell is diffused. This 

 does not render it impossible that at the same time threads of 

 nervous nature may exist, as for example in the case of the 

 innervation of cilia which have to beat at unequal times, as 

 Engelmann believes he observed to be the case in Stylonychia'^ . 

 This assumption also explains how it is possible that 

 swimming colonies of Protozoa are able to perform movements 

 in accordance with a purpose. For example, if we observe 

 a Fo^voic-sphere, which may consist of many hundred indivi- 

 duals, we see that in its movements it behaves no otherwise 

 than as a holotrichous Infusorian ; the sphere swims forwards 

 and backwards, turns in a circle, remains still when necessary, 

 according as some obstacle stands in its way or the course is 

 free. But as the individuals are situated on the surface of 

 a sphere they cannot all strike in the same direction with 

 their flagella, but the movements of these must compensate 



* " Zur ABatomie und Physiologie der Flimmerzelleu," in Piliiger's 

 Arch, fur Physiol, xxii. (18S0) p. 5U5. 



