FLAGELLATA 37 



(1) Principal flagella, which spring from the anterior end of the 

 organism and are projected forwards. They occur singly or in 

 numbers. 



(2) Secondary Flagella. Smaller processes, placed near the true 

 flagella, and likewise occurring singly or in numbers. 



(3) Trailing Flagella. Comparatively long processes which always 

 occur singly. The trailing flagellum starts at the anterior end, 

 generally behind the true flagellum, and it trails behind as the organism 

 swims through the water. These flagella occasionally assume an 

 active part in the phenomena of movement, when they perform 

 jerking movements and so act as a rudder. Some Flagellates are 

 able to bring themselves to an anchor by means of their trailing 

 flagellum. 



(4) Undulating Membranes. This process is found solely among 

 the parasitic members of the group, and it always occurs singly. It is 

 formed by a flagellum, which is attached to the parasite along its 

 length by means of a delicate lamella of protoplasm. The flagellum 

 appears as a thickened edge upon the undulating membrane, and 

 may be continued as a whiplike process beyond it. This is not, 

 however, invariably the case, and the undulating membrane itself is 

 subject to considerable modification. 



The flagellum, whatever its form, is always connected with the 

 nucleus by a characteristic basal structure. At the spot where the 

 flagellum takes its rise, a granule (blepharoblast) is present in the 

 outer layer, which communicates as a rule with the nucleus by means 

 of a strong fibrillum (rhizoblast). In many Flagellates, classed 

 together by Hartmann under the name " Binucleata," there is, in 

 addition to the principal nucleus, a special locomotor nucleus called 

 variously "flagellar-nucleus," ''blepharoblast," or " kineto-nucleus." 



In the life-history of almost all Flagellates, definite periods occur 

 during which there is a temporary degeneration of the flagellate 

 apparatus. This period frequently coincides with the stages of fertili- 

 zation and encysting. The phenomenon has a special significance 

 in the case of certain parasites (particularly the intestinal parasites 

 of insects and the blood parasites of vertebrates) which are able, in the 

 absence of the flagellum, to attach themselves to the cells of their 

 host or even to penetrate to the cell interior. 



Flagellate organisms obtain, their nourishment in a variety of 

 ways. The parasitic varieties feed either by endosmosis (Bodo, Try- 

 panosoma) or by the ingestion of solids (Trichomonas, Triclwmastix) . 

 Those Flagellates which ingest solid food are furnished with a special 

 oral part, the cytostorne (fig. 7, b and c), situated at the anterior 

 end of the body. The methods of nutrition have a practical import- 

 ance in the cultivation of Flagellates upon artificial media. 



