54 PROTOZOOLOGY 



gracilis, Astasia longa and Rhabdomonas incurva, consists of an 

 axoneme, composed of about 9 fibrils, 350-600 A in diameter, ar- 

 ranged in two compact, parallel bundles, and a sheath which is made 

 up of fibrillar elements, a probably semi-fluid matrix and a limiting 

 membrane. Under conditions always associated with death of the 

 organism, the fibrils of the sheath fray out on one or more sides of 

 the flagellum into fine lateral filaments or mastigonemes. The electron 

 micrographs obtained by various investigators on supposedly one 

 and the same flagellate present a varied appearance of the structure. 

 Compare, for example, the micrographs of the frayed flagellum of 

 Euglena gracilis by Brown (1945), Pitelka (1949) and Houwink 

 (1951). The anterior flagellum of Peranema trichophorum frays out 

 into three strands during the course of disintegration as first ob- 

 served by Dellinger (1909) and by several recent observers. It can be 

 easily demonstrated by treating the organism with reagents such as 

 acidified methyl green. Under electron microscope, Petelka noted no 

 frayed mastigonemes in the flagellum of Peranema, while Chen 

 (1950) observed numerous mastigonemes extending out from all 

 sides like a brush, except the basal portion of the flagellum. 



The electron micrographs of the flagellum of trypanosomes reveal 

 that it also consists of an axoneme and a sheath of cytoplasm. The 

 axoneme is composed of a number of long parallel fibrils, 8 in 

 Tnjpanosoma lewisi, each with estimated diameters of 0. 055-0. 06m 

 (Kleinschmidt and Kinder, 1950), and up to 9 in T. evansi, with 

 estimated diameters of 0.04-0.05^ (Kraneveld, Houwink and Keidel, 

 1951). The cytoplasmic sheath of the latter species was said to be 

 cross-striated at about 0.05m intervals. No mastigonemes occur in 

 these flagella. 



The frayed condition of a flagellum which had become detached 

 from the organism or which is still attached to a moribund indi- 

 vidual, as revealed by the darkfield microscope, may also indicate a 

 phase in disintegration of the flagellum. It is reasonable to assume 

 that different flagella may have structural differences as revealed by 

 the electron microscope, but evidence for the occurrence of mas- 

 tigonemes on an active flagellum of a normally living organism ap- 

 pears not to be on hand. 



A flagellum takes its origin in a blepharoplast of kinetosome im- 

 bedded in the cytoplasm. The blepharoplast is a small compact 

 granule, but in certain parasitic flagellates, it may be comparatively 

 large and ovoid or short rod-shaped, surrounded often by a halo. 

 Whether this is due to the presence of a delicate cortical structure 

 enveloping the compact body or to desiccation or fixation is un- 



