of the Desmidiese and Diatomese. 9 



the primordial utricles of the two conjugating Diatoraean cells 

 united ; but that this is not the case, and that a soft and flexible 

 cell-membrane, protruded from the cracked, rigid, old shell, en- 

 closes the contents destined to be blended with those of the 

 neighbouring cell, is distinctly shown by Smith's figure of 

 Rhabdonema arcuatum^ and Carter's of Cocconeis Pediculusf 

 and Amphora ovalis. The introductory part of the conjugation 

 is distinguished in no respect from the vegetative cell-division 

 in Epithemia Sorex, Amphora ovalis and Cymbella Pediculus, and, 

 further, in Closterium rostratum; — in Epithemia turgida, gibba, 

 and verrucosa, only by a different position of the wall dividing 

 the mother-cell ; in the rest of the Diatomese and Desmidiese, 

 by omission of the formation of septa ; frequently, also, by one- 

 sided dehiscence of the cracked mother-cell, whose shells remain 

 still connected at one side. 



Thwaites's observations established that the cell produced 

 from the conjugation of two cells of a Diatomacean, very soon 

 after its origin assumed the form of the mother-cell, becoming 

 distinguishable from it almost solely by being twice as large. 

 Smith has endeavoured to render it probable that the colonies 

 of young individuals, enclosed in a cyst, of Cocconeis Cistula, 

 Gomphonema dichotomum and Synedra radians, some of which he 

 found associated with conjugated, full-grown individuals J, must 

 have originated from the division of the spores (sporanges of 

 English authors). This hypothesis has much in its favour, 

 but in the present condition of our knowledge, it is inexplicable 

 where the siliceous shells of the spore-cells remain. However 

 this may be, there is no doubt of the occurrence of cysts of this 

 kind. In the same pools of a marshy meadow which repeatedly 

 furnished me with conjugated individuals of Cyclotella late in 

 autumn, I found in early spring of two successive years globular 

 cells, each of which enclosed a great number (32 to 40) of small 

 individuals of the same species. The walls of these cells appeared 

 sharply defined internally and externally; the contents of a thin, 

 fluid nature. Structures similar to those represented by Smith, 

 of Synedra radians, occurred in extreme abundance in the end 

 of the autumn of 1854, in company with Synedra Ulna. Here 

 the cells, which, like those observed by Smith in the allied spe- 

 cies, had a diseased aspect and an abnormal arrangement of the 

 coloured contents, were imbedded in a granular jelly, of a red- 

 dish colour by transmitted light. I very much doubt whether 

 these last were in a condition capable of further development ; 

 while in reference to the cysts of Cyclotella operculata, I share 

 Smith's opinion. 



* Smith, h c. pi. E. fig. 305. 



t Annals, ser. 2. xvii. pi. 1. fig. 2. % Brit. Diatomaceae, ii. pi. b. c. 



