208 
cc 
LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’ 
which had developed so far that I judged them to be com- 
pletely formed, because their shells seemed to be perfect. 
I took several thousand of these unborn mussels, and 
put them in a glazed white earthenware basin, and forth- 
with poured canal-water upon them, in order to see 
whether any of these unborn mussels would remain alive 
and grow bigger. 
Having put these little unborn mussels in the water, 
I viewed them on several successive days, yet I could 
make out no change in their size. But since, owing to 
the rain which had fallen plentifully, our canals were 
filled at that time with no other water than what runs 
off the land, and which must then flow through our Town, 
I saw, beyond my expectations, a great many very little 
living animalcules, of divers sorts and sizes, in this water, 
a-swimming among the unborn mussels. Amongst others 
I saw some little worms,’ having a figure very much like 
those worms that children void in their stools,” but whose 
thickness I judged to be a quarter of that of a hair off 
one’s head. 
Furthermore, I saw some animalcules stuck fast to 
one another by their long tails*; and these animalcules, 
as well as sundry other sorts, I had never seen before, and 
their motion was uncommon pleasant to behold. 
Further, I saw that these animalcules did increase in 
numbers from day to day. 
At first, after four or five days, I replenished the water, 
wherein these unborn mussels Jay, in such a fashion 
that I poured off all but about a spoonful* of it, and then 
presently added more canal-water again thereto. 
1 
Probably free-living nematodes. 
* Probably meaning the nematode Oxyuris (=Enterobius) vermicularis. 
3 
Evidently a colonial Vorticellid (Carchesiwm ?). The “ animaleule with 
a tail” is L.’s name for Vorticella, already described in Letter 18 (p. 118). 
Further observations on the colonial forms are recorded later in the present 
letter. (See also p. 277 sq., infra.) 
* op een lepel vol water na Dutch version omnem fere aquam Latin 
translation. 
