44 



MORPHOLOGY OF PROTOZOA 



intracytoplasmic flagellum. The axostyle usually appears as a clear 

 homogeneous structure, but sometimes a fibre has been described as 

 passing along its central axis, while Reuling (1921) has noted that the 

 axostyle of Trichomonas vaginalis may sometimes split into four separate 

 fibrils which originate in the blepharoplasts. He regards the axostyle as 

 composed of four united fibres (Fig. 27). 



MYONEMES.— It may be accepted that one of the characteristics of 

 cytoplasm is its power of spontaneous movement. In many Rhizopoda 

 and Mastigophora there are no visible structures which will account for 

 this movement, which involves a relatively large expenditure of energy. 

 In many Protozoa, however, special con- 

 tractile fibres are developed. An instance 

 in point is the axoneme of a flagellum, which 

 by its contractions causes the flagellum to per- 

 form its lashing movements. Similarly, the 



A B 



Fig. 28. — Myonemes in Gregaeine and Trypanosome. (From Minchin, 1912, 



AFTER Schneider and Minchin.) 



A. Clepsidrina nmnieri. B. Trypamsoma perccB ( x 2,000). 



contractile fibres in the filaments of attachment of certain ciliates, like 

 Vorticella, enable the organisms to withdraw themselves suddenly (Fig. 19). 

 In many of the larger trypanosomes, gregarines, and ciliates there are 

 developed in the ectoplasm a series of fibres of a contractile nature known 

 as myonemes (Fig. 28). These run in various directions, and by their 

 contractions the organisms are able to perform movements of flexion and 

 extension. They not infrequently give rise to a longitudinal marking of the 

 surface of the body. A common type of movement seen typically in gre- 

 garines and merozoites of Sporozoa is the formation of rings of constriction, 

 which pass as peristaltic waves along the body. In certain ciliates para- 



