168 DUBLIN UNIVERSITY 



around it. This hypothesis appeared to be corroborated by the fact that, 

 upon an accurate measurement of the encysted frustules, and compari- 

 son of them with such as were free, they were found to be of exactly the 

 same dimensions. I may add here, that this view of the case was shown 

 to be correct by subsequent observation. 



In the course of the same evening (31st August) I noticed some long 

 filaments of Biatoma vulgare which had folded together in the middle so 

 as to form a compact mass. In some cases a few frustules at either end 

 remained unattached, and these manifested in every case a strong ten- 

 dency to connect themselves with the mass formed by the folding up of 

 the remainder of the filament. One case of this kind particularly at- 

 tracted my attention, in consequence of my noticing at one corner a ge- 

 latinous protrusion, with a clearly defined boundary (Fig. 7). On a very 

 careful inspection of the mass all round, I satisfied myself that there was 

 no appearance of this gelatinous matter, except at the point where I had 

 first remarked it. The importance of this case could not be overrated, 

 as it afforded some hope of a clue to a satisfactory solution of the phe- 

 nomenon. Accordingly, I kept it under notice for some time, and the 

 result was, that I clearly perceived the gelatinous matter pushing itself 

 out, and from the point where I had first observed it, extending itself along 

 the margin of the mass, until, in the space of one hour, the pack of frus- 

 tules was entirely surrounded by a hyaline cyst (Fig. 8), which, with its 

 included frustules, exhibited all the characteristics of variety marked A. 

 This observation rendered it clear that cyst A was the first stage in the 

 process. 



At this stage of the investigation several sporange-like bodies, not 

 seen before, were observed floating about in the water. They consisted 

 of a pellucid envelope, enclosing a large number of granules, accumu- 

 lated towards the centre. These I supposed were the Sporangia of the 

 encysted Diatoma ; but as yet this was merely conjecture, nothing hav- 

 ing as yet come under notice to give to the conjecture the character of 

 fact, or throw light on the process of development, until the evening of 

 the 1st of September, when the investigation was advanced a stage by 

 the observation of a cyst, of the variety described as C. The cyst 

 gradually became more and more elongated, the wall meanwhile at the 

 sides pressing more and more closely on the pack of frustules within as 

 it pursed out at the ends. Into these produced extremities the granular 

 contents of the cyst, which previously had been distributed equally 



