ZOOLOaY AND BOTANY, MICBOSOOPY, ETC. 695 



Cell-division in Closterium.* — A. Fischer has followed closely 

 the process of reproduction by means of cell-division in Closterium, 

 especially in C. Balfsii Breb. f. Delpontii Klebs, and C. moniliferum 

 Ehrenb. f. typicum Klebs. The process of division of the nucleus 

 agrees with that described by Strasburger in the case of Spirogyra. 

 The septum which separates the two halves of the cell is always 

 situated exactly in the middle where the nucleus lies between the two 

 symmetrically arranged chlorophyll-bodies. Before the commence- 

 ment of the formation of this septum and the division of the nucleus 

 into two halves, which then lie on each side of the septum, the cell 

 in all probability becomes slightly constricted, and the entire mem- 

 brane opens by a circular crevice. The process of renewal appears 

 to differ from that observed in other Desmidiese, and varies also some- 

 what in the different species of Closterium. 



The normal process occurs in the first-named species, where the 

 old cell-wall remains unchanged. In the second species, on the other 

 band, the halves of the old cell continue to increase in size, the size 

 of the daughter-cell being in this way influenced. A third type, of 

 periodical renewal, occurs in C. striolatum f. erectum Klebs, where the 

 halves of the old cell develope into new individuals in two distinct 

 periods separated by a period of repose. 



Although these three modes of renewal appear to differ con- 

 siderably at first sight, all three lead to the same result, the isolated 

 cell-halves developing into a new individual, resembling as closely as 

 possible the parent generation. The mode of division of the nucleus 

 and chromatophores is the same in all three types. The nucleus 

 appears to undergo a second transference, apparently passive, and 

 reaches the new cell-half, in which it takes up its permanent position. 

 The two portions of the chlorophyll-body develope into two perfect 

 chromatophores, each occupying one-half of the new individual. The 

 variability of form within the same species of Closterium is probably 

 due to variations in the mode of renewal, which may also account for 

 the occurrence of transitional forms. 



Sections of Diatoms.t — W. Prinz criticizes the remarks of E. W. 

 Burgess on this subject,j which were based on the deeper colour of 

 the centre of the areolae of certain diatoms. 



" It might be hoped," says M. Prinz, " that the images due to 

 effects of diffraction would no longer serve to support the hypothesis 

 of elevations on the surface of certain diatoms. I think it useless to 

 recall the theoretical explanations given specially for Goscinodiscus 

 Oculus-Iridis by Stephenson, or the more general considerations 

 developed in the works of Professor Abbe. It is sufficient to know 

 that the Eadiolaria, whose perforations are admitted by all observers, 

 present exactly the same dark spots in the centre of the pores which 

 traverse them. 



This discussion has lasted nearly fifty years; and we shall 



* Bot. Ztg., xli. (1883) pp. 225-35, 241-7, 257-66, 273-5 (1 pi.)- 

 t Bull. Soc. Belg. Micr., ix. (1883) pp. 124-6. 

 X See this Journal, ante, p. 264. 



