ZOOLOGICAL AND BOTANICAL ASSOCIATION. 167 



a frustule of Synedra radians included. I had before this noticed cysts in 

 which frustules of Colletonema subcoherens and ftfelosira variant seemed 

 to be included; but the hypothesis of Smith exercising an influence on my 

 mind, I was disposed to consider that these foreign forms, which seemed 

 to be folded within the cysts of Diatoma vulgare, might possibly be ad- 

 hering to the outer surface of the cell- wall. No doubt, however, could 

 exist as to the fact of the frustule of Synedra radians being not adherent 

 to the outside of the cyst, but actually included within it, because the 

 shape of the cyst was such as to show that in its formation it had accom- 

 modated itself to the shape of the Synedra. Usually the wall of the 

 cyst did not extend much beyond the frustules included, and at all 

 points was at an equal distance from it ; but in the case I now refer to, 

 the frustule of Synedra extended at either end considerably beyond the 

 mass of the frustules of Diatoma, and the cyst had thrown itself out be- 

 yond the usual limits, narrowing beyond the boundary of the mass of 

 Diatoma so as barely from that out to cover the extremities of the Syne- 

 dra (Fig. 6). Nor was this observation a solitary one, very many cases of 

 the same nature having occurred. Also, several cysts of Synedra radians 

 were noticed, in which frustules of Diatoma vulgare, in greater or less 

 numbers, were included. 



This fact seemed to indicate that if Smith's hypothesis concerning 

 the case of Cocconema cistula were correct at all, it could not apply to 

 the case of encysted* Diatoma vulgare that had come under my notice, 

 without supposing that different species might result from the conjuga- 

 tion of the same parent frustules. Such a view is so contrary to the 

 analogy of nature, that nothing short of actual observation could warrant 

 its entertainment. 



I was, therefore, disposed to doubt the correctness of Smith's hypo- 

 thesis, at least so far as it might apply to the case before me, and to con- 

 sider that the encysted frustules of Diatoma vulgare, instead of being the 

 product of a Sporangium, were the parent frustules in the conjugated 

 condition, from which the Sporangium was to be the ultimate result. 



According to this view, the inclusion of foreign forms within the 

 cysts— a matter of very frequent occurrence — might be easily explained 

 by supposing that when the frustules came into the state of conjugation, 

 the foreign forms which chanced to be in proximity were drawn in with 

 the mass, and ultimately included within the cyst which was formed 



ZOOL. & BOT. SOC PKOC. VOL. I. 2 A 



