ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 731 



family AuricuKdae is the genus Pedipes, in which the partitions were 

 found intact. The absorption is not always complete, nor are the 

 same parts invariably missing. Complete absorption was observed 

 in Melampus, Auricula, Blauneria, Marinula, Tralia, Alexia, Monica, 

 Plecotrema ; only partial absorption in Cassidula and Scarabus. The 

 case of Olicella is more remarkable, since the allied groups Oliva, 

 Ancillaria, &c., do not, according to the authors, present this 

 peculiarity at all. Tryon, however, observes * that in Oliva reticularis 

 he has found the walls absorbed away, so that very little of the sub- 

 stance remained, and considers it probable that all shells with close 

 volutions are in the habit of absorbing them internally. It is 

 certainly the case with many of them. 



Development of the Digestive Tube of Limacina.t — S. Jourdain, 

 having reminded us that the first indication of the pharyngeal 

 vestibule of the Limacina appears as an invagination of the vitelline 

 mass, and that, later, another invagination, which corresponds to the 

 anal opening, appears in the middle line, between the two external 

 openings of the segmental organs, now tells us that the base of the 

 pharyngeal invagination is continuous with a cavity, the walls of 

 which are mesodermal and are lined by endodermal cells. The diges- 

 tive tube has, at this period, the form of a sac ending in a spherical 

 diverticulum, which will become the gland that is incorrectly spoken 

 of as the liver. This gland has at first a mesodermal and an endo- 

 dermal origin ; the framework being formed of mesoderm, and the 

 secreting tissue of endoderm. The hepatic tissue is filled with a 

 finely granular fluid, which is coagulated by heat, alcohol, or nitric 

 acid, but does not lose its transparency ; it is a kind of secondary 

 yolk, the quantity of which increases rapidly during the early periods 

 of embryonic development, and which fills the digestive tube. It 

 probably arises from the elaboration of the albumen of the egg and 

 is digested by the embryo during its development. 



The internal wall of the alveoli of the hepatic sac gives rise to 

 cells by budding ; these cells gradually take on the characters of the 

 secreting elements of the liver, so that each alveolus becomes a lobe 

 of the hepatic organ. This organ ought not to be called a liver : it 

 is only a diverticulum of the stomachal portion of the intestinal tract. 

 It performs so many functions that it would be better spoken of as a 

 chylific gland. Moreover, its mode of development may explain the 

 bizarre forms that it sometimes attains, as for example, in the 

 Eolidije, where we may suppose that each of the alveoli of the organ 

 became isolated, acquired a great size, and took the form of the varied 

 appendages which are found in those Gastropoda. 



MoUuscoxda. 

 Simple and Compound Ascidians.J — W. A. Herdman is unable 

 to find a single satisfactory character by which to distinguish simple 

 from compound Ascidians. Reproduction by gemmation and the 



* Man. Couch. : Olivella, p. 64. 



+ Couiptes Rendua, xcviii. (1884) pp. 155.S-6. 



; Nature, xxix. (1884) pp. 429-31. 



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