Organisms Consisting of One Cell 253 



The flagclliim marks the anterior end of the creature; and along 

 with it there is an undulating membrane, the two forming an 

 efficient locomotor apparatus. 



The explanations accompanying figures 7 and 8 name the parts 

 of the system. Special attention may be called to the following 

 points : 



The nucleus, u, with its distinct membrane, central karyosoine, 

 and clear space between the latter and the membrane; the 

 hinetonucleus (always written with quotation marks by Miss Mc- 

 Culloch, for reasons which we shall mention later) ; the rhizo- 

 plast, a fine thread connecting the karyosome of the nucleus with 

 the kinetonucleus; the ha^al granule with its numerous very fine 

 connections running to the kinetonucleus ; and the a.rostyle, a 

 thread extending from the basal granule to the posterior end 

 of the body. 



Concerning the function of all these parts our knowledge is 

 very fragmentary. The reader should never forget the diffi- 

 culty of observing these organisms. The largest individuals of 

 this species are 40 or about 1/625 of an inch long, and as 

 the figure shows, narrow in proportion to the length. Because 

 of this minuteness several of the parts, for example the rhizo- 

 plast and the various granules, are at the very limit of visibility 

 by the best microscopes. This fact, combined with the peculiar 

 conditions under which the animals live, make it impossible to 

 study a single individual during its whole life or even a con- 

 siderable portion of it. Probably the impossibility of studying 

 the parts as they do their work is chiefly responsible for the 

 meagerness of w^hat we know about the functions of the organs. 

 The nucleus of a large number of protozoans, including this one, 

 is often called a trophonucleus from the theory that it is chiefly 

 concerned with nutrition. 



The term kinetonucleus has been a])plied to the organ thus 

 labelled from the conjecture that it has specially to do with 

 the movements of the animal. As the figure shows, the flagellum 

 is connected, though indirectly, with this organ, and this means 

 that the undulating membrane is also related to it. But the 

 fact that there are plenty of flagella and undulating membranes 

 in other species which have no kinetonucleus, makes it certain 

 that its role in the production of motion can not be exclusive 

 or very fundamental. Concerning the office of the several gra- 

 nules, the rhizoplast and the axostyle, nothing positive seenas 



