234 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Melosira Borreri , and Gallionella nummuloides. In the first-named 
species the process differs from that in other Naviculeae in that the 
two conjugating individuals always place themselves with their valve- 
sides next one another. Gallionella exhibits a departure from Pfitzer’s 
statement that in the Melosirese each of the cells which goes to the for- 
mation of an auxospore has first been formed by division. In this 
instance the nucleus passes from the older into the younger cell. The 
mode of formation of the auxospores in the Melosirese coincides with that 
in Synedra affinis, with only unimportant differences. It is, in fact, a 
modification of the process of cell-division. 
In Synedra affinis two auxospores are formed from each cell by 
longitudinal division. Each auxospore has two well-developed nuclei,, 
each with a large nucleole. In Brebissonia Bceclcii the two conjugating 
diatoms are always so placed that their girdle-bands lie side by side or 
one on the other. In Achnanthes brevipes two mother-cells take part in 
the formation of each auxospore. The author believes that in all cases- 
the formation of an auxospore is but a modified form of longitudinal 
division, conjugation of the daughter-cells of two individuals taking the 
place of the conjugation of nuclei within one and the same individual. 
He argues in favour of the near relationship of the Diatomaceae to the 
Desmidiem. 
The author distinguishes two types of auxospore-formation in dia- 
toms : — (1) That of the Melosireac, in which the auxospores are formed 
by the agency of a single cell-division, usually greatly reduced ; (2) that 
of the Naviculeae, Cymbelleae, Achnantheae, and Fragilarieac, in which a 
double cell-division takes place, the second division being often reduced. 
He derives the conclusion that originally diatoms multiplied only by 
division, and that the formation of auxospores is a mode of increase and 
rejuvenescence derived from a purely vegetative multiplication in two 
different ways. 
Structure, Division, and Movements of Diatoms.* — Herr R. Lauter- 
born publishes a detailed treatise on the structure of the protoplasm in 
diatoms, especially in reference to the division of the nucleus and of the 
cell. The “ red corpuscles ” are regarded as reserve-substances employed 
by the cell for building up new matter, as, e.g., in the process of cell- 
division. The centrosome has been observed in other species besides- 
the one in which it was originally detected, viz. in Surirella splendida,. 
S. biseriata, Pinmdaria major, and P. nobilis. The division of the nucleus 
and of the cell are described in detail in several species, especially in 
Surirella calcarata, where the process attains a great degree of com- 
plexity. The paper is accompanied by a careful bibliography. 
Dr. 0. Miillerf criticises in several points Lauterborn’s explanation of 
the causes of the movements of diatoms. He regards the movements a& 
taking place by means of currents of a mucilaginous substance project- 
ing through the raphe on to the outer cell- wall. He has never seen any 
trace of the threads described by Lauterborn as springing from the 
central node. 
* * Unters. iib. Bau, Kernlheilung, u. Bewegung d. Diatomeen,’ Leipzig, 189G,. 
165 pp., 10 pis., and 2 figs. See Bull. Soc. Beige de Microscopic, xxi. (1897) p. 27. 
Cf. this Journal, 1894, p. 606. 
t Ber. Deutseli. Bot. Gesell., xv. (1897) pp. 70-8. • 
