128 ELECTRON-MICROSCOPIC STRUCTURE OF PROTOZOA 



the two flagella, one of them bears the swelling known as the 

 paraflagellar body (p. 24). The broadly expanded flagellar 

 membrane here encloses a low-density space containing irregular 

 patches of material, and a large (up to 1-5 /z), dense, ovoid mass. 

 Beneath the adjacent wall of the reservoir is the cresent-shaped 

 cluster of pigment-containing stigma granules. 



From the bases of both kinetosomes, tubular fibrils pass out in 

 various directions. At least some of these are continuous with the 

 fibrils underlying the reservoir membrane and thus, presumably, 

 with the fibrils of the pellicle system. 



The disc-shaped chloroplasts of E. gracilis have regular, parallel 

 bands of lamellae ; each contains a pyrenoid consisting of a dense 

 matrix traversed by thinner bands. Paramylum bodies typically 

 are ranged on both surfaces of the pyrenoid regions of the 

 plastid but outside its membrane ; apparently they are not enclosed 

 in membranes of their own. Like starch, they have a very low 

 density in electron micrographs. The euglenid eyespot is unusual 

 in being separated from any chloropList; it is considered to be an 

 entire modified plastid, but no observations on its ultrastructure 

 during development have been reported. 



The numerous, small, spheroid or rod-shaped mitochondria of 

 Euglena have distinct cristae; often these project radially inward 

 from the inner limiting membrane (see Fig. 4, PL I). Well- 

 developed Golgi bodies, consisting of eight to 20 packed sacs with 

 peripheral microvesicles, are distributed throughout the cell. The 

 cytoplasmic matrix contains an abundance of Palade particles, 

 and smooth endoplasmic reticulum. Conspicuous large vacuoles 

 containing scattered vesiculate, very dense conglomerates are 

 identified by Gibbs as metachromatic granules, or volutin. In 

 E. viridis (de Haller, 1960), peripheral vesicles containing a 

 dispersed coagulum of moderately dense material represent the 

 mucigenic bodies, which are absent from E. gracilis. 



The Euglena nucleus has a typical fenestrated double envelope 

 with a highly irregular contour. The nucleoplasm is densely 

 granular, with compact clumps interpreted by Ueda (1958) as 

 sectioned chromonemata. The large persistent nucleolus or 

 endosome is finely granular in texture, and denser than the nucleo- 

 plasm. Gibbs (1960) pictured an ovoid body consisting of three 



