82 



THE SMALLEST LIVING THINGS 



tions are correlated and the organism acts as a unit. Each indi- 

 vidual is attuned to a certain "motor response" to any stimulus 

 from the environment. If the stimulus is applied to some local 

 part of the organism the part stimulated does not respond locally, 



ani. cyi 



mot. 



1.cX 



a.c.f. 



v. c. ■ 



.--■m.c. 



Fig. 47— THE NEUROMOTOR 

 SYSTEM OF EUPLOTES PATELLA 



a.c, position of the anal cirri; a.c.f., co- 

 ordinating fibers from anal cirri to mo- 

 torium, mot; ant. cyt. f., co-ordinating 

 fibril to anterior lip and down to the mouth. 

 Fibers from the ventral cirri, v.c. ; mar- 

 ginal cirri, m.c; and frontal cirri, f.c. 

 do not connect with the motorium but end 

 blindly in the protoplasm 



After Taylor 

 Magnification, 510 



but the stimulus is transmitted to all parts and a characteristic 

 response on the part of the organism results, regardless of the 

 nature of the stimulus. 



Nuclei 



Another structural characteristic distinguishes the derived 

 adult organization of infusoria from all other protozoa. This 

 is the presence of two kinds of nuclei, one large and of highly 

 varied shapes, the other small and spheroidal; the former is 

 called the macronucleus, the latter the micronucleus (see Figures 

 46-48). The larger one functions in vegetative activities, the 

 smaller one in cell division and in sexual processes. 



Cell Division 



Reproduction occurs by transverse cell division, during which 

 the complex structures of the derived organization are resorbed* 

 and new ones are formed by each daughter half (Fig. 49) . Divi- 



* Resorbed, drawn or sucked in. 



