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One parasomal sac lies anterior to each basal body of the somatic
ciliature. A parasomal sac is an indentation of the plasma membrane
that penetrates into the cytosol past the alveolus. Most sacs end as a
coated pit (arrowhead). However, as seen in this micrograph
(arrows), they can also give rise to more extensive tubules and
vesicles. These vesicles pinch off into the cytosol to become early
endosomes in a process called endocytosis where they lose their coat
and fuse with a flattened smooth-membraned cisterna that is the early
endosome. lip, lipid droplet. EM taken on 7/17/67 by R. Allen
with Philips 200 TEM. Neg. 9,000X. Bar = 0.5µm.
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