MORPHOLOGY AND HISTOLOGY OF THE DIGESTIVE-TRACT OF NAUTILUS-POMPILIUSAND NAUTILUS-MACROMPHALUS (CEPHALOPODA, TETRABRANCHIATA)

This study presents histological and scanning electron microscopical f indings on the structural differentiation, and the nervous and vascula r supply of the digestive tracts of Nautilus pompilius and N. macromph alus, including the foregut, stomach, vestibulum, caecum, midgut and r ectum. The stereoscopic reconstruction of the vestibulocaecal complex gives an idea how the digestive cycle between the stomach, vestibulum, caecum and proximal midgut could possibly proceed. All parts of the d igestive tract are covered luminally by a columnar epithelium which co ntains numerous goblet cells. The epithelium is ciliated in the vestib ulum, caecum, proximal midgut and the longitudinal groove of the rectu m. On this lamina epithelialis mucosae borders the lamina propria muco sae, which consists of connective tissue and some muscle cells. In the stomach it is differentiated, forming a special bolster-like layer. T he lamina propria mucosae is followed by the tunica muscularis, which consists of a stratum circulare and a stratum longitudinal in the fore gut, vestibulum, caecum, midgut and rectum. In the stomach, midgut and rectum, the tunica adventitia, which consists of a thin layer of conn ective tissue, is located between the tunica muscularis and the cuboid al tunica serosa.