50 Mr. William Ingrams. 
stone, found in the neighbourhood, in our underground 
circulation contains many pebbles, and also, owing to an 
obstruction, a great quantity of the same material which 
has cemented into a consolidated matrix the whole of 
what were centuries since free pebbles. This will be quite 
sufficient to show that water which has percolated through the 
earth contains silex in solution. The water issues from 
springs perfectly clear and pure, and from it the diatom 
secretes what is held in invisible solution—the silex which 
forms the epiderm of the cell. The silex secreted consists of 
two parts called valves, separated by a line. The valves at ° 
times separate, and what appears to be a line becomes a band 
or hoop, wider and wider, till at length it is, in some cases, 
cast off, leaving two separate individual cells. This process 
is called binary sub-division. It is not peculiar to the diatom, 
but exists also in confervoid and other growths. This may be 
called a system by which the species is increased by gemmina- 
tion in contradistinction to that above described by germination. 
There is yet another peculiarity by which the species is dis- 
tinguished. Two individual cells in contact open, and the 
whole contents of each flow out, become amalgamated, and 
form a cell twice the size of the parent cells. This process 
is called conjugation. It is very remarkable, and if it were 
the ordinary mode of increase would lead to the production of. 
a giant race. Time would fail to go into this part of the 
subject. It is fascinating certainly, but it does not account for 
the presence of the infant diatoms. 
One word more as to the provision for the preservation of the 
species. At certain seasons, none better than April and May, 
the microscopist will be watching with curious eyes the move- 
ments in his drop of water of the naviculoid forms and their 
cargoes, and it may be also the vibrations of Gomphonema or 
Synedra splendens, and will be much disappointed when, just as 
he is about, he thinks, to see what he has so long watched for 
take place, the discharge of endochromous granular particles, 
to find his drop of water has evaporated. He should, just 
before this takes place, when what little water remains is drawn 
by attraction to the diatoms and surrounds them, so that he 
cannot see them distinctly, do one of two things, and each with 
a different object in view. He should, if he would:see his pets 
a little longer, with a delicate touch, allow a small drop of water 
to issue from a very fine-pointed dipping tube to the circular 
space occupied by the first drop; or notice, with thrilling 
interest, the provision made for the preservation of the species. 
Slowly but surely, the anxiously-expected, long-looked-for 
granules and bubbles of protoplasm will retreat, if the species 
be straight and tubular, as in Synedra splendens, and attached 
