42 



M0RPH0L0C4Y OF PROTOZOA 



regarded as external skeletons or supports. These various structures 



are secreted by the cytoplasm, from which they are separate. In all 



Protozoa which have a distinctive body form it is the rigidity of the 



ectoplasm which enables the organism to retain its shape. In certain 



cases, what may be regarded as 



modifications of the cytoplasm are 



developed for purposes of support. 



Thus, in certain Ciliata, as, for 



instance, Prorodon, the anteriorly 



placed cytostome leads to a cyto- 



pharynx which is supported by a 



series of longitudinally arranged 



rods (Figs. 24 and 25). These rods, 



or trichites, can be drawn apart and 



the cytostome opened by radially 



arranged contractile fibres attached 



to each rod. In connection with the 



cytostome of certain Mastigophora, 



such as Chilomastix, the margin of 



the cytostomal groove which leads 



to the cytostome is supported and 



rendered rigid by special fibres 



(Fig. 69). In Trichomonas, again. 



Fig. 25. — Section through Cyto- 

 stome OF Prorodon teres, showing 

 Supporting Rods ( x ca. 600). (From 

 MiNCHiN, 1912, after Maier.) 



N, Nucleus; R, rods; ;«.?-. and m.r.', 

 myonemes. 



Fig. 26. — Trichomonas {Pentatricho- 

 monas) from the Human intestine 

 ( X 3,200). (After Kofoid and 

 SwEZY, 1924.) 



the line of attachment of the undulating membrane is supported by a 

 special basal fibre which takes origin in a blepharoplast, and appears to 

 function by keeping the membrane stretched to its full extent (Fig. 26). 



Another structure which also occurs in Trichomonaf! and allied forms 

 is the axostyle. This is a stift rod which commences in the blepharoplasts, 



