402 SUMMARY OF CURRENT RESEARCHES RELATING TO 



8- Lamellibranchiata- 

 Mucous Cells in Mussels.* — Dr. B. Kawitz has found in the 

 mantle of Mussels goblet-cells, of which some are small, with a largo 

 central nucleus and granular protoplasm ; others are large, with a small 

 central nucleus, the rest of the cell-contents being uniform in appear- 

 ance ; and others again are large, with a small nucleus situated at the 

 base of the cell, the protoplasm having oily granules scattered through- 

 out itself. This last kind of cell allows the oily granules and mucous 

 contents to pass out at the apex of the cell into the surrounding water. 

 A careful investigation has shown that the above three different kinds 

 of cells are merely different stages in the secretory activity of the 

 mucous cells, and that during this activity the cell-contents not only 

 undergo a change of minute structure, but also of chemical composition, 

 the latter being evidenced by the changed reactions which they give 

 with staining agents. During secretion the cell itself is not broken 

 down, but only a portion of its protoplasm is excreted in the form of 

 oily drops and mucous threads, the nucleus remaining intact. Dr. 

 Rawitz considers that special importance must be assigned to the 

 nucleus in connection with the nutrition of the call, as during the 

 secretory activity of the cell it undergoes changes, not only in its shape, 

 but in its behaviour towards staining reagents. 



Striated Muscles in Mollusca. — M. R. Blanchardf thinks that 

 Prof. Fol cannot have fully carried out the proper means of investigating 

 the structures of the muscular tissue of Molluscs, or he would not have 

 denied the presence of striated fibrils. J He calls attention to his account 

 of the muscles of Pecten, and asserts the accuracy of his observations on 

 the true transverse striation which can be seen in that form. 



M. L. Roule§ has reinvestigated the subject and confirms Fol 's obser- 

 vation. In muscles which exhibit contractions of some amplitude (e. g. 

 the retractors of the shell), it may be seen that during extension the 

 fibres have their fibrils parallel to their longitudinal axis, while during 

 contractions the fibrils become spirally twisted. Fol's note seemed to 

 indicate that the spiral state was constant, whereas it is only exhibited 

 in contracted fibres. The author suggests that the same state of affairs 

 may possibly obtain in the case of some Annelids and other Vertebrates 

 where transverse striag have been described. 



Molluscoida. 

 #. Bryozoa. 



Nervous System of Phylactolaematous Fresh- water Bryozoa. [| — 

 Dr. A. Saefftigen has a preliminary notice on the Dervous system of these 

 Bryozoa, based on a study of Cristatella and Plumatella. He finds that 

 the cavity of the supra-oesophageal ganglion is not completely sur- 

 rounded by nervous elements, for on the side which is turned towards 

 the oesophagus there is endothelium. The nervous elements of the 

 ganglion consist of a cortical layer of cells, bounded externally by endo- 

 thelium, and inclosing a fibrous mass, which in transverse section is 



* Nature, xxxvii. (1887) p. 168, from Proceedings of Berlin Physiological 

 Society, 1887, Nov. 18. f Comptes Rendus, cvi. (1888) pp. 425-7. 



X See this Journal, ante., p. 190. § Comptes Rendus, cvi. (1888) pp. 872-4. 



|| Zool. Anzeig., xi. (1888) pp. 96-9. 



