164 BIOLOGY OF THE PROTOZOA 



Like the majority of formed organoids of the cell, the more com- 

 plicated of the motile organs described above are formed anew at 

 each division of the cell. This does not apply to the majority of 

 pseudopodia nor has it been observed in the case of cilia, but is 

 well-established for flagella and for the aggregates of cilia, such as 

 membranelles, undulating membranes and cirri. In a few cases 

 the flagella themselves are said to divide, but this is questionable, 

 the flagella probably arising in all cases from the substance of 

 blepharoplasts or basal bodies which have divided. Young (1922) 

 has shown that a cirrus of Uronyckia transfuga if cut does not 

 regenerate, but if the protoplasm is partly included in the opera- 

 tion a new cirrus is regenerated. Demboska (1925) has shown that 

 if a single cirrus of Stylonychia is cut out all of the cirri are renewed. 

 (d) Oral and Anal Cortical Modifications. In all naked forms 

 of Protozoa and in corticate forms which, like Opalina, take in food 

 substances by osmosis through the general body surface, there are 

 no portions of the ectoplasm differentiated as cytostomes or cell 

 mouths. In such forms, furthermore, where there is no undigestible 

 matter, there is no modification as cytopyge (cytoproct, or cell 

 anus). In testate forms, obviously, there is only a limited region of 

 the body substance which is open for the reception of food. In 

 testate rhizopods the shell openings are due to the physical condi- 

 tions under which the lifeless shell materials are deposited and no 

 definite mouth parts as protoplasmic differentiations are present. 



In all Protozoa, on the other hand, which take solid food and 

 which are covered by more or less highly differentiated cortical 

 plasm, there are permanent openings in the cortex serving for the 

 intake of solid bodies and for defecation of undigested remains. 

 In many cases such openings in the cortex merely expose a limited 

 region of soft receptive protoplasm as in Oikomonas termo (Fig. 

 97, B, p. 186), but in other cases complicated cortical differentia- 

 tions with supporting and food-procuring adaptations give rise to 

 complex and permanent cytostomes and cytoprocts. 



In flagellates such an area of softer protoplasm is situated at or 

 near the base of the flagellum, or two such areas may be present, 

 each at the base of a flagellum or group of flagella, as in Trepomonas 

 and Ilexamitus. In one group, the Choanoflagellidae, a collar-like 

 membrane arises as a protoplasmic fold around the base of the 

 flagellum and forms a cuff or funnel surrounding the flagellum 

 for a distance equal to one-third or one-half its length (Fig. 92). 

 These are extremely delicate, the margins alone in many cases 

 indicating their presence and dimensions. According to France, 

 they are somewhat spirally rolled like a cornucopia, the free mar- 

 gin arising from the softer food receptive area and by its move- 

 ments directing food particles toward this area. This, according 

 to de Saedeleer (1929), is an erroneous interpretation, the appar- 



