Organisms Consisting of One Cell 253 



The flngcllum 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, n, with its distinct membrane, central karyosome, 

 and clear space between the latter and the membrane; the 

 kinelonucleus (always written with quotation marks by Miss Me- 

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

 /)!(!*(, a fine thread connecting the karyosome of the nucleus witli 

 the kinetonuclcus; the basal granule with its numerous very fine 

 connections running to the kinetonuclcus ; and the axostyle, 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 10 or about 1/62/5 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 rhi/o- 

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

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

 conditions under which the animals live, make it impossible to 

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

 sul, rah!', portion of it. Probably the impossibility of studying 

 parts as they do their work is chiefly responsible for the 

 gerness of what we know about the functions of the organs, 

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

 often called a troplionucleus from the theory that it is chiefly 

 cerned with nutrition. 



The term k'nictounclens has been applied to the organ thus 

 abelled 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 flagclla 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 rhi/oplast and the axostyle, nothing positive seems 



