166 DUBLIN UNIVERSITY 



I referred to Smith's work on the Diatomaceaj, and in the plates of the 

 second volume found described two cases similar to that which had just 

 come under my own observation — one of Synedra radians, the other of 

 Cocconema cistula ; and in the preface, where he refers to the phenome- 

 non of encysted diatoms, were the following remarks : — 



" In the gathering of Cocconema cistula made in April, 1852, which 

 contained numerous instances of the conjugating process, I observed the 

 frequent occurrence of cysts enclosing minute bodies, variable in their 

 number and size, and many of which had the outline and markings of 

 the surrounding forms, and were obviously young frustules of the Coc- 

 conema. These cysts and their contents are figured in Plate C, 221, 

 III., IV. and V. It would appear from these figures that the production 

 of the young frustules is preceded by the separation and throwing off of 

 the siliceous valves of the sporangium, and the constriction or enlarge- 

 ment of its primordial utricle, according to the number of young frustules 

 originating in its protoplasmic contents. In this gathering, forms of 

 every size intermediate between the minutest frustule in the cyst, and 

 the ordinary frustules engaged in the conjugating process, were easily to 

 be detected ; and the conclusion was inevitable, that the cysts and their 

 contents were sporangia of the species with which they were associated, 

 and indicated the several stages of the reproductive process." 



It is obvious from the above quotation that Smith's opinion in the 

 case of Cocconema cistula was, that the encysted frustules were the infant 

 condition of the organism — a step in the process of development from the 

 sporangium produced by the conjugation of the parent frustules. In 

 this opinion Hoffmeister, in a paper of his on the " Propagation of Des- 

 midiae and Diatomeae," published in the January Number of the " Annals 

 of Natural History" for the current year, seems to concur. " Smith," 

 he says, "has endeavoured to render it probable that the colonies of 

 young individuals enclosed in "a cyst of Cocconema cistula, Gomphonema di- 

 chomum, and Synedra radians, some of which he found associated with 

 conjugated, full-grown individuals, must have originated from the divi- 

 sion 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." 



I was not disposed to question the correctness of an hypothesis resting 

 on such authority until the 31st of August, when, on examining a drop 

 from the gathering, I observed a cyst of Biatoma rulyare (Fig. 5), with 



