Gastropod gill morphology 5 
rinsed again in phosphate buffer, dehydrated in a graded series of ethanols, and embedded in Spurr's 
epoxy medium (Spurr, 1969). Ultrathin sections were cut on a LKB UM III, and stained with lead 
citrate and uranyl acetate (30 s Pb — 60 s UA — 30 s Pb) (Daddow, 1983). The sections were 
examined with a Hitachi H300 transmission electron microscope at 75 kV. 
Light Microscopy: The excised gills were rinsed in freshly filtered seawater, before being fixed 
overnight in 10 % neutral buffered formalin. The next day the gills were washed in distilled water, 
then dehydrated in a graded series of ethanols (70 %, 90 % and 100 96, for periods of 30 minutes 
each). This was followed by two thirty minute periods of immersion in toluene, after which the gills 
were embedded in wax. Subsequently, 6 um thick sections were cut on a Spencer Rotary 828 
microtome. After completion of the cytochemical tests the sections were examined and photographed 
under an Olympus light microscope fitted with a photo-automat. 
Cytochemistry: Schiff's periodic acid test was performed on 6 um thick light microscopic sections to 
determine the presence of mucopolysaccharides in secretory cells (Lillie, 1964). Ayoub-Shklar's 
(1968) method for keratin and prekeratin was performed on 6 um thick light microscopic sections to 
establish the type of connective tissue present in the gill filaments. Mayer's haematoxylin — eosin 
alcoholic stain was used when preparing routine overview sections. 
Figurel. LM micrograph of the gill of Austrocochlea constricta. The nature of the connective tissue was determined 
with Ayoub-Shklar's (1968) method for keratin and prekeratin. The largest proportion of the connective 
tissue consists of collagen (c), which stains darkest. The somewhat lighter stained areas surrounding the 
collagen consist of prekeratin (p). 
