LETTER 96. MUSSEL-WATER 215 
taken from the surface of that wherein the mussel lay, a 
vast company of living animalcules: but to make sure of 
this, | made use of a glass of higher magnification, and 
a different instrument: and I then saw so great a many 
of such extreme small animalcules,’ that there’s no man 
living could possibly conceive of them; nay, they were so 
little, that several millions of them together would not be 
as big as a coarse grain of sand. Nevertheless, all these 
animalcules, when I put them in a glass tube, remained 
alive but a little while. 
Moreover, I found that the animalcules in the water 
that the mussel was in, had increased so much in seven 
or eight days, that I might well say their number was (to 
the best of my judgement) quite ten times a hundred 
thousand more than those in the water before I put the 
mussel in it. 
Regarding this increase of animalcules in water, and in 
so very short a time, I have oft-times been amazed: and 
especially, because I chanced to see divers sorts of 
animalcules, which increased in numbers, without being 
able to discern any of them that were smaller; all of 
them being of an equal bigness.” 
But after observing what I have just related (namely, 
that there are animalcules which do not take to swimming 
about till they have reached their full growth, and 
which soon after are ready to copulate; and therewithal 
that a full-grown animalcule is produced in one night), I 
was now, to my great satisfaction, delivered from all 
those difficulties, that I had for years laboured under, 
concerning the generation of these little creatures. 
When I first discovered, in the year 1675, a great 
plenty of divers very little animalcules in water, and 
made these observations known by letter to the Royal 
’ Bacteria. 
* He means that he could detect no young ones of any species. 
