8 W. Hofmeister on the Propagation 



Cyclotella operculata, conjugation-cells of which, with adherent 

 empty coats of the mother-cells, I found abundantly in ditches 

 of a marshy meadow not far from Leipsic, in October 1852. 

 They were not distinguishable in any essential respects from the 

 Cyclotella Kiitzingiana figured by Thwaites. 



Next to these cases of the formation in the first place of only 

 one conjugation-cell, come a series of observations in which two 

 new cells were seen between the empty conjugated mother-cells, 

 without any convincing evidence being offered of a division of 

 the mother-cells having occurred just before conjugation, as in 

 the cases hereafter to be mentioned ; — where rather the position 

 of the empty cells in relation to the conjugation-cells, and the 

 affinity of the forms in question to some in which the entire 

 development has been observed, render it probable that the uni- 

 cellular condition of the conjugation-cell has hitherto escaped 

 observation. In this group are to be counted Cocconema lanceo- 

 latum^, Cocconema Cistula, Gomphonema dichotomum, lanceola- 

 tumf, marinumX, Achnanthes longipes^, Rhabdonema arcuatum\\, 

 Colletonema subcohcerens. 



In a smaller number of Diatomese, species of the genera, so 

 nearly allied together, Epithemia, Cymbella, dindi Amphora^, i\i.Q 

 conjugation is immediately preceded by a division of the mother- 

 cells into two, analogous to the division of the cells of Closterium 

 rostratum when about to conjugate. This division is longitudinal, 

 taking place exactly as in the vegetative division in Cymbella 

 Pediculus^*, Amphora ovalisff, and Epithemia SorexfX, but 

 transverse and in a direction crossing that of the vegetative 

 division in Epithemia turgida, gibba, and verrucosa ^^. 



Recent observations show distinctly that the conjugation of 

 the Diatomese agrees in all essential points with that of the 

 Desmidiese. When a cell is about to conjugate, there is pro- 

 duced in it a coat round the entire contents, accurately lining 

 the old membrane, but not adhering to it. The growth of this 

 coat cracks the old cell- membrane exactly in the same way as 

 occurs in vegetative division. From the fissure the young, smooth 

 coat emerges, in the form of a vesicle, and unites with the 

 similar structure produced by a neighbouring cell. Al. Braun || || 

 thought it must be assumed, from Thwaites's observations, that 



* Thwaites, Annals, xx. pi. 22. fig. c. Smith, /. c. pi. c. fig. 248. 



t Smith, I. c. pi. c. J Ibid. pi. d. fig. 246. 



§ Ibid. pi. D. fig. 300. II Ibid. pi. e. fig. 353. 



% Ibid. pi. E. fig. 353. 



** Carter, Annals, 2 ser. xvii. pi. 1. fig. 17. tt Ibid. fig. 23. 



XX Smith, I. c. pi. A. fig. 9. i. 



§§ Thwaites, Annals, xix. Smith, /. c. pi. a. 



nil Al. Braun, Verjungung, p, 305 (Translation, p. 285). 



