STRUCTURAL DIFFERENTIATIONS 155 



Adinoholus radians, these suctorial tentacles are retractile, but 

 again there is no satisfactory explanation of their activity and no 

 description or mention of speciaHzed motile apparatus. 



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 probabh- arising in all cases from the substance of 

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

 has recently shown that a cirrus of Uronychia transfiicja if cut does 

 not regenerate, but if the protoplasm is partly included in the 

 operation a new cirrus is regenerated. Demboska has still more 

 recently (1925) shown that if a single cirrus of Stylonychia is cut 

 out all of the cirri are renewed. 



(f/) Oral and Anal Cortical Modifications.— In all naked forms 

 of Protozoa and in corticate forms which manufacture their own 

 food as in the phjiioflagellates or which, like Opalina, take in food 

 substances by osmosis through the general body surface, there are 

 no portions of the ectoplasm differentiated as c}i;ostomes or cell 

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

 matter, there is no modification as cytopyge, or 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. 

 88, B), but in other cases complicated cortical differentiations 

 with supporting and food-procuring adaptations give rise to complex 

 and permanent cytostomes and c\1:oprocts. 



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 Treyomonas 

 and Hexamitiis (Fig. 88, p. 179). In one group, the Choanoflagel- 

 lidffi, 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. 82). These are extremely delicate, the margins alone in 



