Within the shell, the mantle is very thin, semi-transparent and colourless apart from a faint, fine, pale-grey speckling. Where it roofs the mantle cavity , it contains many haemolymph vessels and is very thin, enabling oxygen from inhaled air to diffuse into the vessels and for carbon dioxide to leave with the exhaled air.
The residual mass is squeezed from the stomach as faecal boli into the intestine by muscular contractions and passes to and through the rectum.The rectum and part of the intestine, runs along the rear edge of the roof of the mantle cavity to the anus .
1: haemolymph vessels visible against grey speckling.
2: as 1, magnified and colour contrast increased.
3: stomach.
4: intestine full of material.
5: empty rectum (no clear division between intestine and rectum, but matter travels faster through the rectum).
6: anus
7: digestive gland.