MORPHOLOGY OF MELIBE 549 



' Into the posterior part open four or fi\e liver-ducts and also 

 a pear-shaped gastric pouch, whose orifice in the stomach-wall 

 is closed with a more or less distinctly developed flap. This 

 pouch is often called the gall-bladder, but nothing indicates 

 that its functions correspond to this name. Its walls are 

 glandular, and appear to secrete globules of a glistening material 

 which is also found in the intestine. It is possible that this 

 secretion subsequently dissolves and forms a membrane which 

 is found to cover the walls of the stomach and intestine, and 

 probably serves to protect these delicate surfaces against the 

 spicules abounding in the sponges on which most Dorids feed.' 

 Finally, Arnold (1916: 353-4), referring to the Cla do- 

 ll e p a t i c a , thinks that the liver, which in most nudibranchs 

 is extremely large and completely surrounds the stomach, 

 in Dendronotus also extends into the dorsal cerata 

 (papillae), so that they may have some digestive function. 



The hepatic diverticula of M. leonina consist structurally 

 of two main layers : an outer fibrous coat and an inner 

 columnar epithelial membrane. The fibrous layer, consisting 

 of connective tissue, is thrown into corrugations — inwardly — 

 so that the surface of the lumen of the hepatic appendages is 

 greatly increased (PI. 33, figs. 51, 53). The cytoplasm of the 

 epithelium is highly glandular and one may notice considerable 

 variation in the contents of the cells. Some of the cells show 

 a similarity to the ' Keulenzellen ' of Frenzel, or ' Cellules 

 vacuolaires excretrices ' of Hecht. In fact, as is shown in 

 PL 33, figs. 48, 49, 50, some of the cells have large vacuoles 

 containing granules of different sizes (PL 33, figs. 48-9), and 

 some are vacuolated and contain no granules, while others 

 have no vacuoles but their cytoplasm is highly granular. 

 Others, again, show a remarkable linear arrangement of the 

 granules, liasal to the nucleus (PL 33, fig. 49). The greatest 

 activity of the cell seems to take place around or near the 

 nucleus with a progressive differentiation toward the border, 

 where the cell in many cases is more homogeneous than in the 

 remaining part. Sometimes a large secretion vacuole may 

 contain threads of darkly stained substances with a darkly 



