ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 53 



proposed to call " marcnnin," which is diifused through the proto- 

 plasm ; when this blue marennin is deposited in the yellowish-brown 

 gill-filaments of the oysters, it has a greenish hue ; there can be no 

 doubt that marennin derived from N. ostrearia, taken as food, is 

 present either unchanged or slightly modified in the gills of the green 

 oyster, and is the cause of the colour. The pigment is localized in 

 certain peculiar cells of the superficial epithelium of the gills and 

 tentacles, viz. in the large subspherical " secretion cells," which are 

 placed at intervals among the more numerous smaller columnar cells ; 

 this is possibly the only known instance of a pigment introduced 

 through the alimentary canal being eliminated by gland-cells in an 

 unaltered condition. 



Cephalic Appendages of Gymnosomatous Pteropoda.* — Dr. P. 



Pelseneer has investigated the cephalic appendages of Clione, Clionopsis, 

 and Pneumodermon, the homologies of which are very obscure. There 

 are always two pairs of tentacles, and the author does not think it rash 

 to identify them with the two pairs of the euthyneurous Gastropods ; 

 in the Thecosomata there is a pair of rudimentary tentacles, and if 

 they do not possess eyes when adult they have them in some stage of 

 their development ; these correspond to the posterior or nuchal 

 oculiferous pair of tentacles in the Gymnosomata, while the dis- 

 appearance of the anterior is to be explained by the swimming lobes 

 encircling the head. Most of the Gymnosomata have a pair of buccal 

 appendages between the two pairs of tentacles, and these, though 

 varied in aspect, are probably similar in origin ; it is explained, how 

 in Clione they are really inserted on the external wall of the buccal 

 cavity just as in Cirrifer and Pneumodermon ; but at the same time 

 it is to be remembered that this part of the buccal cavity is an 

 " introvert," and not a true part of the oral cavity. 



Molluscoida. 

 o. Tunicata. 



CynthiidsB of the Coasts of France.f — MM. H. de Lacaze- 

 Duthiers and Y. Delage have examined the simple Ascidians which 

 belong to the group of the Cynthiida3 chiefly by the aid of Cynthia 

 morus, which is very abundant at various places on the coasts of 

 France. They describe its external appearance and the differences 

 in expanded and contracted forms ; the spines appear to be poly- 

 morphic, but there is one character which is very useful in diagnosis, 

 the microscopic bodies which are found on the internal surface of 

 its orifices. If a small piece of the epidermis be cut out and ex- 

 amined under the Microscope, one can in all cases detect a rounded 

 projecting scale, which is similar in the most dissimilar-looking 

 individuals. 



After describing in detail the anatomy of the type, the authors 

 point out the affinities which exist between the Cynthiidaa and the 

 Molgulidae ; these are to be found in the characters of the mouth and 



* Quart. Journ. Micr. Sci., xxv. (1885) pp. 491-509 (1 pi.), 

 t Comptes Rendus, ci. (1885) pp. 784-90. 



