580 SUMMARY OF CURRENT RESEARCHES RELATING TO 



its nuclear division granules appear ou the network and become larger 

 and fewer, while the nucleolus disappears ; these stages are obscure, but 

 probably the chromosomes are being formed on the spireme. Then 

 about twelve short broad chromosomes are seen collected on the 

 equatorial plate ; fibres, but no definite spindle, can be made out. 

 Tiiese stages are all figured, also the metaphase, anaphase, telophase. 

 In the daughter-nuclei the chromosomes disappear, granules appear 

 and gradually fuse to form the large nucleolus. The daughter-nuclei 

 move asunder at once and become situated opposite the pyrenoids. 

 Formation of the new cell- wall was not observed in detail ; but it is 

 always completed before the division of the chromatophore begins. 

 As the chromatophore divides the nucleus slips in between the two 

 halves until it finally reaches the pyrenoid and, during the division of 

 the pyrenoid by constriction, remains firmly pressed up against it. 

 Division of the chromatophore and pyrenoid is probably largely 

 influenced by the presence of the nucleus. The starch sheath of the 

 pyrenoid is not markedly affected until chromatophore division begins ; 

 the starch sheath then rapidly sinks and disappears. The presence of a 

 large store of starch in the cell is not in itself sufficient to induce 

 nuclear division. 



Piunularia.* — X. E. Brown describes and figures the plan upon 

 which Pinnidaria is built, giving first an account of the structure of the 

 silicious skeleton, based chiefly upon observations made upon P. major, 

 P. nobilis and P. gentilis ; and, secondly, recording such observations 

 as he has made upon living specimens. He describes the structure in 

 plain language, explaining the meaning of the technical terms. He 

 points out that the costge are not solid, but " sausage-shaped cavities in 

 the substance of the cell-wall, separated from each other by a thin plate 

 of silex." The presence of these large cavities with the large opening 

 into the interior distinguishes Pinnidaria from Navicula. The walls of 

 these cavities are described, and also a structure which the author 

 believes to be pores, extending along the centre of their outer wall. 

 The conclusion of the paper is to follow. 



Fresh-water Diatoms.t — V. Torka writes on the diatoms of the 

 great Jesuit Lake near Bromberg. In the mud was found Mastogloia 

 baltica Grun., hitherto recorded only from brackish water, and 

 M. elliptica var. Dansei, which occurs in fossil strata in Mexico. 

 M. Smithii is found, but more rarely. Navicula vulpina is figured here 

 for the first time, and the characteristic points of its structure are 

 shown. Forty-three of the species here recorded have been found in 

 the interglacial moor strata of Posen ; and since most of the others are 

 still found in living form in West Prussia, it is concluded that the 

 " Faulschlamm " of Schilling, near Posen, originated from a lake 

 similar to those still existinfj. 



■O' 



* Journ. Micrology, No. 15 (1916) pp. 35-40 (figs.). 



t Ber. Westpreups. Bot. Zool. Verein Danzig, xxxvii. (1915) pp. 332-6 (2 figs.). 

 See also Bot. Centralbl., cxxxii. (1916) p. 207. 



