For each individual digestive gland, a total of 50 tubule sections were drawn with the
aid of a drawing tube coupled to a Nikon Optiphot microscope. We used an objective
lens of 3100. Five sections were randomly selected from each 10 paraffin section
belonging to two different portions of the gland (50 mm apart). The profiles of the 50
sections were recorded with a Watanabe DT1000 digitizer and the resulting planimetric
measurements were calculated with a personal computer following the method of
Marigo´mez (1989) which is based in the geometrical transformation of the tubule
section shapes. Two parameters are obtained: mean diverticular radius (MDR) and mean
epithelial thickness (MET).