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CHAPTER 4 
THE LATER OBSERVATIONS ON FREE-LIVING 
PROTOZOA 
(LETTERS 122, 125, 144, 147, 149, 150, VII, X XIX) 
Leeuwenhoek in his’ multifarious  protistological 
wanderings during the last quarter of the X VII Century. 
We have yet to consider his equally remarkable excursions 
into similar unexplored fields at a later date. 
At the turn of the century—when he was already an old 
man, nearing his 70th birthday—he was still, despite his age, 
at the height of his powers; and during the next few years— 
between 1700 and 1716—he recorded some of his most 
interesting protozoological discoveries. These observations 
were all made on free-living forms found in water. 
In a letter written at the very beginning of 1700, 
Leeuwenhoek gave the first description and picture of 
Volvoz. The letter’ begins with an account of other observa- 
tions, and describes inter alia some gnat-larvae which he had 
found in ditch-water.? It then proceeds : 
Ie the three preceding chapters we have followed 
IT had got the foresaid water taken out of the ditches 
and runnels on the 30th of August:* and on coming 
1 Letter 122. 2 January 1700. To Sir Hans Sloane. MS.Roy.Soe. 
Published [Dutch] in Brieven, III, 152 (2nd pagination), Sevende Vervolg 
(1702): [Latin] in Opera Omnia (Epist. Soc. Reg.), III, 146 (1719) : English 
translation in Phil. Trans. (1700), Vol. XXII, No. 261, p. 509.—Curiously 
enough, Vandevelde entirely overlooks the fact that this letter contains the 
first description of Volvoz. 
2 These observations are also remarkable: for they show that L. had 
noticed the difference in posture of Anopheline and Culicine larvae in the 
water—a peculiarity now well known, but generally supposed to have been 
discovered by recent malariologists. 
* Anno 1698, as appears from the earlier part of the letter. 
