of the Desmidicie and Diatomctc. 9 



the primordial utricles of the two conjugating Diatomcan cells 

 united; but that this is not the ease, and that a soft and tiexible 

 cell-nuMnbrane, protruded from the cracked, riirid, old shell, en- 

 closes the contents destined to be blended with those of the 

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

 Rlutbdunema arcuatum* and Carter's of Cocconeis Pei/iculusf 

 and Amphora oralis. The introductory part of the conjugation 

 is distinguished in no respect from the vegetative cell-division 

 in Epithi'mia Sorex, Amphora ova/is and Cijinbella Pediculus, aiul, 

 further, in Closterium rostralum; — in Epithemia turgida, gihha, 

 and verrucosa, only by a different ])Osition of the wall dividing 

 the mother-cell ; in the rest of the Uiatomeie and Desmidicfc, 

 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 produee<l 

 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, 

 Gumphonema dichotomum and Sijucdra radians, some of which he 

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

 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 uo doubt of the occurrence of cysts of this 

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

 furnished me wdth conjugated individuals of Cyclotella late iu 

 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 a])peared 

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

 fluid nature. Structures similar to those represented by Smith, 

 of Stjnedra radians, occurred in extreme abundance in the end 

 of the autumn of 1854, in company with Si/nedra 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, /. c. pi. E. fig. .305. 



t Annals, ser. 2. xvii. pi. 1. fig. 2. % Bnt- Diatomacea?, ii. pi. b. r. 



