SOME PROBLEMS IN THE PHYSIOLOGY OF THE PROTOZOA 303 



an oxygen-free medium. Enucleated pieces in the ordinary medium 

 will live, but those in the oxygen-free medium quickly die, showing 

 that oxygen-taking is possible without the nucleus. So, too, the con- 

 tractile vacuole continues to pulsate in Amceba even nine days after 

 the operation which separated it from the nucleus (Hofer). 



The nucleus, furthermore, appears to have nothing to do directly 

 with the functions of irritability, for non-nucleated fragments respond 

 as readily to stimuli as do the nucleated parts. They show the same 

 chemotactic, thermotactic, and galvanotactic reactions as the complete 

 organisms, and Eimer's view that the nucleus is the seat of psychic 

 activity as expressed by motion, is flatly contradicted (Verworn, '89). 



Perty ('52), as well as Dujardin ('41 ), long since questioned the intel- 



A 



B 



Fig. 152. — Isolated nucleus of Thalassicolla nucleata Hux. [VERWORN.] 

 A, B, C, D. Regenerative changes. £, F, G, H. Degenerative changes. 



ligent power of the Infusoria in their reactions to stimuli, and more 

 modern observers have generally accepted the view that the proto- 

 plasm of these animals responds automatically, in greater or less 

 degree, to stimuli of various kinds. In the Sarcodina, the entire cell 

 is equally irritable ; but higher in the scale, the outer plasm becomes 

 more and more sensitive in relation to the entire body until, in the 

 membranes of Infusoria, a generally sensitive skin is found which is 

 sometimes drawn out into so-called sensory processes (feelers and 

 tasters of hypotrichous forms), while in the Mastigophora special 

 sensory or receptive spots are frequently present (" eye-spots "). This 

 tendency to localization of the sensitive parts of the protoplasm is 

 only in accord with our a priori conceptions of differentiation brought 

 about by reaction to the environment or adaptation, and is strictly 



