Beprodudion & Multiplication of Diatoms. By Count Castracane. 23 



I desire more than to be convinced when I am in error ; and if it is 

 shown to me that I have not offered sufficient proof of any of my 

 opinions, I will endeavour to give more forcible and convincing argu- 

 ments for them. Having had the high honour of being elected an 

 Honorary Fellow of your Society, I venture to hope that the Society 

 will examine and discuss my views on a subject so important and so 

 strictly germane to its scope ; and with this object I will endeavour 

 to give as clear and concise a resume of them as possible. 



Diatoms, like all vegetable organisms, are reproduced by con- 

 jugation or bisexual fecundation, and are multiplied by deduplication 

 or autofission. Keproduction is common to all living organisms, but 

 multiplication by fission belongs only to some organic types ; thus all 

 diatoms are reproduced as a consequence of fecundation, while only 

 certain generic types exhibit multiplication by fission. 



Speaking in the first place of multiplication by deduplication ; 

 this process, actually observed in many cases, has been claimed to 

 be a general one, as if it were common to all diatoms. It is well 

 known that this process commences with the subdivision of the 

 nucleus and of the cytoblast, followed by the bipartition of the proto- 

 plasmic sac by the formation of a double wall which extends to the 

 centre from the inner periphery of the connecting ring, constituting 

 two new valves, each of which is in front of one of the primitive 

 valves. The fact that this ring is double, or rather is composed 

 of two zones, each of which proceeds from one of the valves, and 

 one of them inclosing the other, constitutes the emboitement of 

 diatoms which, if not absolutely common to all types, is evident in 

 many genera. It is therefore strange that so acute and careful an 

 observer as W. Smith, notwithstanding that, especially in the figures 

 of the Naviculacese, he indicates by a double line on the zonal side 

 the extreme edge of the two rings, yet has no clear idea of them ; 

 since, instead of recognizing, as the consequence of the deduplication, 

 the progressive diminution of the frustules, he speaks of the increase 

 in size of the young frustule resulting from the fission.* 



The most exact description of the constitution of the diatom-cell, 

 that of Dr. E. Pfitzer, in his work, ' Untersuchungen iiber Bau und 

 Entwicklung der Bacillarien,' also demonstrates, with the help of 

 diagrammatic figures, how the process of autofission leads necessarily 

 to a decreasing scale of magnitude in the offspring, until so minute a 

 size is reached as to be incompatible with the biological conditions of 

 the species. In this I agree altogether with Pfitzer, if, in truth, the 

 diatom within its siliceous walls is incapable of increase in size and 

 of the widening of its walls so long as they are under the influence of 

 life. Although this property has been attacked by some, I am unable 

 to understand the disinclination to admit a fact about which there does 

 not seem to me the least doubt. 



In 1874 there was held in Florence an International Botanical 



* * Syuopsia of British Diatomaceee,' i. Introduction, p. xxvi. 



