MARINE AND ESTUARINE DIATOMS. 
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visible together with the “ connecting membrane,” this is known 
as the “ front ” or “ zonal ” view. 
The multiplication of Diatoms is by one or other of two 
processes, both common to all the lower forms of vegetation. 
The first of these is “ by division,” the second “ by conjugation.” 
When a Diatom is about to multiply by “ division ” two new 
valves, are formed within the old one, applied back to back, and 
each united with one of the old valves by a new “ connecting 
membrane,” and as this grows and elongates, the old “ connect- 
ing membrane ” is ruptured and falls off, leaving two new 
individuals where previously there was only one. The new 
individuals thus formed may remain adherent to each other, 
wholly or partly, or may become entirely free as already described. 
In some instances they remain embedded in a sort of gelatinous 
envelope or enclosed in gelatinous tubes. The process takes 
place simultaneously in many cells (or frustules as they are 
technically termed) and with comparative rapidity, thus account- 
ing for the vast number of individuals usually found associated 
together. “Conjugation” on the other hand is a comparatively 
rare process and has actually been observed only in a relatively 
small number of species. In this case, much as in Spirogyra, a 
common water plant, often known as Pond Scum, two cells or 
frustules, lying side by side, mingle their contents ( endochrome ) 
to form one or two reproductive bodies, known as sporangia, 
usually much larger than the two cells from which they are 
derived, and which will eventually by “division” form new 
frustules similar to those from which they were derived. This 
process, however, is but very imperfectly understood. Single 
individuals of adjacent chains may be “ conjugating ” while the 
others are multiplying by ordinary “ division.” So rapid is this 
latter process that it has been estimated that one thousand 
millions of new individuals may be produced in a single month. 
The Diatoms are essentially aquatic, and are to be found in 
all waters, fresh or salt, to which light has access. They are, 
however, most abundant and most varied in sea water, while 
estuaries, like the Kennebecasis, and marshes and creeks to 
