204 
F. KANSOM—DIATOMS: 
(Anderdank) in the ‘ American Monthly Microscopical Journal ’ for 
1883 to the effect that the movements are due to what he terms a 
“ mobile pallium ” which partially surrounds the frustule. This 
lie describes as “no mere theory , v having stained, detached, and 
mounted many of these gelatinous envelopes. Another hypothesis, 
suggested by negative rather than positive results, is that the motion 
is entirely due to purely mechanical forces, such as heat, light, and 
capillarity. 
Although the motion of diatoms is slow compared with that of 
many of the animal organisms with which they are found, it is not 
insignificant if regarded in relation to their size. The most rapid 
in movement is Bacillaria joaradoxa , which Smith found to proceed 
at the rate of about an inch in three minutes. It has been calcu¬ 
lated that a snail crawling at the same proportionate rate for its size 
would traverse half a mile in an hour. 
Another subject of interest in connection with the natural history 
of diatoms, and requiring further investigation, is that relating to 
the methods of reproduction. The simplest and most usual mode 
is self-division, corresponding with the ordinary cell-division as seen 
in all branches of the Yegetahle Kingdom^ The first step of the 
process probably consists in the division of the interior protoplasm 
by a growth of cellulose. This is soon followed by the develop¬ 
ment of two fresh siliceous valves exactly similar in structure to 
those of the original frustule, and growing up opposite to each in 
the interior of the cell. As soon as these new valves are fully 
developed, the frustule (if that of a free species) splits from end 
to end, and two diatoms result, each possessing one of the original 
and one of the newly-formed valves. The time occupied by a 
healthy and vigorous frustule for one such process has not been 
definitely determined, but is estimated by Smith to be about 
twenty-four hours. Supposing this to be correct, a simple cal¬ 
culation will show that the progeny of a single organism in a 
month of thirty-one days will amount to upwards of 1,000,000,000. 
Although it is not probable that the conditions would be sufficiently 
favourable to secure such a result, the fact will help to explain the 
remarkable increase in diatoms which may frequently be seen in a 
puddle of rain-water that has remained undisturbed for a few days. 
Another method of reproduction consists in the conjugation of two 
frustules, when remarkable changes take place. The protoplasmic 
contents of each appear to unite; a membranous bag is developed 
around them, which resolves itself into a sporangium, and, various 
changes having occurred, several fresh frustules finally result. 
Yarious modifications have been observed in the process according 
to the species examined. 
In estimating the results produced by diatoms in the economy of 
Mature, we find that the imperishable character of the siliceous 
valves plays an important part. In most parts of the world where 
search has been made, large deposits of so-called fossil diatoms have 
been discovered. "Whether fossil, or even sub-fossil, is a correct 
term to apply to these remains, when, as is frequently the case, 
