548 H. p. KJERSCHOW AC4ERSB0RG 



through the ectoderm (PI. 27, tigs. 1, 2, 4, 7 ; PL 81, tig. 80), 

 but caecally between it and the muscle-wall (PI. 27, figs. 2, 3). 

 Frenzel (1886 : 273) l)eheved with other authors that the Kver 

 of molluscs performs a double function : (1) as in Crustacea 

 it is a digestive gland, ' d. h., dass sie ein Secret bildet und 

 ausscheidet, welches zur Verdauung der in den Darmkanal 

 aufgenommen Hpeisen verwendet wird.' (2) In addition, this 

 gland is according to Max Weber (1880) for the Crustacea, 

 and according to Barfurth (1 883) for the Gasteropoda, of 

 ' excretorische Function '. They think that the liver of these 

 forms is analogous to that of vertebrates. They describe cells 

 that have special functions, such as secretory and excretory. 

 Frenzel points out three kinds of epithelial cells of the liver 

 of Tethys: (1) ' Kornzellen ', (2) ' Keulenzellen ', (3) ' Kalk- 

 zellen '. To these different cells he ascribes the various func- 

 tions of the organ. These cells are further described by Hecht 

 (1895 : 675), as follows : ' La presence de trois types bien 

 definis de cellules : (1) Cellules vacuolaires excretrices carac- 

 terisees par leurs grandes dimensions et leurs grandes 

 vacuoles (Frenzel : Fermentzellen, Keulenzellen) contenant 

 chacune une granulation. . . . ; (2) Cellules excretrices a grosses 

 spheres brunes (Leberzellen, Kornzellen) ; (3) Cellules a 

 ferments. Leur coloration en gris par les reactifs osmiques ; 

 on y joindra ; (4) Cellules indifferentes qui, je le suppose, 

 peuvent evoluer dans un sens ou dans Tautre." The structure 

 and function of the liver in a Doridiform clado hepatic 

 nudibranch, is still further commented on by Eliot and 

 Evans (1908) as follows : ' The cells which line the hepatic 

 lobules are columnar or cuboidal and highly granular. Some 

 are in a distended condition, others are attached to the w^all of 

 the. lobule only by a strand or are free in its cavity. It would 

 seem, therefore, that some of the liver cells are excretory in 

 function, and are dropped into the follicle as they become 

 extended with excreted material.' Eliot (1910 : 39) attributes 

 to the liver the function which, in the case of M. leonina, 

 I have shown to be the function of the epithelium of the 

 posterior chamber of the stomach, i.e. the gizzard, viz.: 



