640 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Glands of Aplysia and allied Forms * — F. Blochmann deals with 

 the glands found at the edge of the mantle in Aplysia and some of 

 its allies, attracted to the study by the presence, in A. limacina, of 

 gigantic unicellular glands, which may be as much as 1 mm. in length. 

 The basis of the edge of the mantle, like the whole of the body- wall, 

 is formed by the. peculiar laminar tissue which is so widely distri- 

 buted among the Mollusca. Externally this is limited by a uni- 

 laminate cylindrical epithelium, the cells of which are pigmented. 



The glands now to be mentioned are imbedded in the connective 

 tissue, and they may be regarded as (1) simple, (2) as more compli- 

 cated purple-glands, and (3) as the analogous glands which produce 

 a milky secretion. They are all unicellular, and the simple have the 

 form of the so-called goblet cells. These are filled by a clear mucous 

 secretion, such as is also found in some pyriform glands, which are 

 most common on the upper side of the mantle. Another form of 

 unicellular gland, which is seen in A. depilans, is greatly elongated, 

 and the contained protoplasm has a large number of secretion- 

 granules. The narrower end serves as an efferent duct, and appears 

 to be provided with a membrane. This kind of cell was found to 

 be, in all cases, limited to the lower side of the mantle, and placed 

 between the large purple-glands ; they were best developed in A. 

 punctata, where the purple-glands are considerably diminished in size 

 and number. In Dolabella dolahrifera we find, in addition to the 

 unicellular glands, multicellular ones, which are remarkable for con- 

 sisting of two continuous layers of cells, of which those lying next 

 to the efferent ducts are smaller, and contain cleai-er protoplasm than 

 those of the outer layer. 



The glands which secrete the purple-colouring and milk-like 

 substance are particularly interesting, inasmuch as we have here to 

 do with comparatively complicated organs, which are essentially uni- 

 cellular in structure. Not only is the secretory function performed 

 by a single giant-cell, but the ectodermal invagination gives rise 

 to a multicellular efferent duct. The structure of these bodies is 

 investigated, and their development is reported to be of the fol- 

 lowing character ; the glands arise from epithelial cells, which, sud- 

 denly increasing in size, push their way into the connective tissue, 

 without, however, losing their connection with the outer world ; a 

 cavity is only gradually developed in their interior, and they seem, 

 at first, to be provided with a membrane, no indications of which are 

 to be seen in the adult. An investment of connective tissue cells is 

 gradually formed around the gland-cells. 



Sexual Characters of Oysters.f — J. A. Eyder treats of the micro- 

 scopic sexual characters of the American, Portuguese, and common 

 edible oyster of Europe, pointing out that, until recently, he had 

 " maintained with reservation that the sexes in the European oyster 

 were probably separate, as in the American " ; a greater refinement of 

 method has shown the author that ho was in error. 



* Zeitschr. f. Wiss. Zool., xxxviii. (1883) pp. 411-8 (1 pi.), 

 t Ann. and Mag. Nat. Hist., xii. (1883) pp. 37-48. 



