550 H. p. KJERSCHOW AGERSBORG 



staining cap toward the periphery. Such threads may be 

 present in the cell without the cell being vacuolated. The 

 secretion product, at other times, aggregates from a number of 

 small vacuoles at the border of the cell and passes out en 

 masse, when it seems to be basic in staining reaction. That 

 is, the basophil reaction is shown in material which has been 

 fixed in an osmic acid mixture and stained with Heidenhain's 

 haematoxylin. The nucleus, as a rule, is basal in position 

 and contains one or two nucleoli (PI. 33, fig. 48). The morpho- 

 logical aspect of an actively functioning liver of Physa 

 gyrina Say, and Planorbis trivolvis Say, does not 

 differ much from that of Melibe leonina (Gould) (vide 

 Agersborg, 1923 a, figs. 35, 36, 38, 41, 42). It is not my purpose 

 at this time to discuss the function of the hepatic system of 

 M. leonina; but it is eA'ident from the facts observed, and 

 as pointed out above, that at least some of its products passes 

 into the stomach, and for this reason it is secretory in function. 

 Perhaps, owing to the peculiar granular nature of the cytoplasm 

 of the epithelial layer, it may be absorptive in function also. 

 In that connexion it is interesting to note the extensive 

 distribution of the liver to the various organs of the body, the 

 significance of which at the present time may only be con- 

 jectured. The peculiar granular nature of the cytoplasm of 

 the epithelium shows that its function is different from that 

 of the epithelium of the alimentary tube proper. 



7. The Circulatory System. 



The work of Milne Edwards (1842) on Aeolidiidae; 

 Alder and Hancock (1845) on the Aeolidiidae and 

 T r i t o n i i d a e ; Hancock and Embleton (1 848) on A e o 1 i d i a , 

 (1881) and (1882) on Doris; Hancock (1865) on Doris 

 tuberculata, D. reponda, D. bilamellata, Tri- 

 ton i a h m b e r g i i , B o r n e 1 1 a , and S c y 1 1 a e a ; Bergh 

 (1875) on Melibe and Tethys, (1884a) on M. papillosa ; 

 Lansberg (1882) on Neritina; Boas (1886) on Pteropodes 

 (Limacina, and Cleodora acicula); Sedgwick (1888) 

 on Per ip at us, (1898) on gasteropods ; Bouvier (1891) on 



