26 Transactions of the Society. 



cyst, as may be seen on Plate B in Synedra radians W. Sm., and on 

 Plate C in Cymbella (Gocconema) cistula Hemp. 



It has been proved by Eabenhorst's observations on Melosira 

 varians Ag. and O'Meara's on Pleurosigma Spencerii W, Sm., as 

 well as by similar observations of my own on a Podosphasnia, that 

 these round and well-defined corpuscles must be considered as sporules 

 or gonidia, whether they are inclosed in the sporange as in the case 

 above mentioned, or whether they occupy the whole or a part of the 

 cavity of the normal sporangial frustule, as may be seen in some of 

 the figures in the plates to which reference has been made. In all 

 these cases these corpuscles were seen to escape from the mother-cell, 

 as represented by Eabenhorst in fig. 18, pi. x. of his ' Die siisswasser 

 Diatomaceen.' I, being unable to draw, have described the whole 

 minutely, pointing out that these corpuscles are marked by very 

 fine lines, a proof of the presence of an inclosing membrane ; and 

 that, turning round at the moment of their escape, they present a 

 profile alternately round and linear, which prevents the possibihty 

 of their being monads or similar Infusoria. "While preparing a 

 monographical work on a very interesting Italian deposit from the 

 middle Miocene, I have already met with four specimens of Cos- 

 cinodiscus punetulatus Ehrb., which show how death overtook 

 them at the moment when they were giving birth to a numerous 

 progeny. In fact my frustules with radiating dots are seen to be 

 surrounded by numerous round impressions, which cannot be re- 

 garded in any other light than as sporules or embryonal forms, 

 destined to develope and to grow while reproducing the typical form. 

 This has demonstrated to me, in opposition to my previous view, that 

 diatoms contain silica even in the embryonal condition — at least that 

 this is the case with Coscinodiscus punetulatus, as otherwise these 

 impressions could not have been preserved. 



If I am asked what is my view of the process of reproduction in 

 diatoms, I reply, without the least hesitation, that the processes may 

 be— and in fact are— very different according to the genus, even if not 

 also according to the species. I have myself seen several of these 

 processes, and I therefore wish to guard myself altogether from being 

 drawn on to generalize by starting from any special case, however 

 well established, even when such generahzation should agree with 

 my preconceived ideas. It is necessary that such a rule be constantly 

 observed in undertaking any new researches, for, in the adoption of 

 a provisional hypothesis for the purpose of grouping together isolated 

 facts, the progress of our knowledge would be at least retarded if the 

 provisional hypothesis were regarded as an established fact. 



The extraordinary advance of geology during recent years, in 

 consequence of the gigantic works in opening canals, in making 

 entrenchments, and in piercing mountains for the establishing of new 

 roads of communication, and the frequent marine expeditions for 

 scientific purposes, have induced microscopists to occupy themselves 

 almost exclusively with the discovery of new types of diatoms. But 

 how much more important is the daily observation of the diatoms 



