72 
The Presidenfs Address. 
species I quite concur ; but this peculiarity of structure is by 
no means so singular as the author appears to imagine, neither 
do I think he has quite correctly interpreted the appearance 
presented — of course, not having seen the specimen itself, I 
may be in error — but I think it but reasonable to direct 
attention to what I consider a very frequent peculiarity of 
structure — somewhat difficult of demonstration, it is true, in 
ordinary cases, but thereby affording more zest in the pursuit, 
and an admirable exercise of manipulatory ingenuity. This 
same structure, but on a scale considerably more minute, I 
detected, and subsequently exhibited at a soiree given by this 
Society some years ago, in a specimen of Triceratrum favus, 
obtained from Ichaboe guano. I published no record of it, 
and therefore am the more pleased at a corroboration of my 
observations, by finding the same design upon a larger scale. 
Since detecting it in the Triceratrum favus, I have also been 
able to demonstrate the existence of it in every specimen of 
Coscinodiscus radiatus upon which I have attempted the 
feat ; and this has been done on those obtained from various 
sources, viz., the stomach of a muscle, guano, the mud of the 
Thames, Barbadoes fossil, &c. 
Now with respect to the interpretation of the structure. 
In describing the Arachnoidiscus, in one of the early volumes of 
the ^ Transactions' of this Society, I showed that the frustule 
consists of a siliceous framework, over which is stretched a 
species of membrane, whether siliceous or not I do not presume 
to decide, but certainly pliant to a considerable extent, capable 
of being partially rolled up by mechanical agency without 
breaking, and elastic enough to return to its original 
position when the extraneous force is removed. Now the 
structure noticed by Mr. Roper, in Coscinodiscus labyrinthus, 
and by myself in the more common species — C. radiatus and 
Tr. favus — I believe to be of precisely the same natm^e, and I 
am much mistaken if we do not find it in many other species 
of the Diatomacese. 
Mr. Roper's observations of structure in what he has 
termed Actinocyclus triradiatus are also well worthy of 
special attention. I may remark, en passant, that I dis- 
sent from the opinion that the frustule named belongs to the 
genus cited. 
Before quitting the Diatom acese, I would also direct at- 
tention to Mr. Ralfs' interesting paper in the last October 
number of the ' Journal,' concerning one of the modes of re- 
production prevalent in some genera of this natural order. 
We have had one paper, a very important one, belonging 
to the class of experimental physics, entitled, Precise Direc- 
