Lysosomes were stained following the method of Moore (1976) as described in
Cajaraville et al. (1991) which is based on the cytochemical reaction for b-glucuronidase.
The enzymatic reaction yields a purple-colored product. Light microscopic images
were then obtained by coupling an image processing system comprising a B&W-CCD
TV camera, a HR-TV colour screen and a personal computer (AT-PC), to the Leitz light
microscope and using an objective lens of 3100. The area corresponding to the
lysosomes in purple colour and the rest of cytoplasmic matter of the digestive cells were
manually segmented by assigning them different colours on the monitor. Computerized
measurements of the areas corresponding to different colours allows computation of the
following parameters (Lowe et al., 1981): lysosomal volume density (VD, lysosomal
volume/ cytoplasmic volume), lysosomal numerical density (ND, number of lysosomes/
cytoplasmic volume), lysosomal surface density (SD, lysosome surface / cytoplasmic
volume) and the surface to volume ratio of the lysosomes (S/V).
2.3. Digestive