20O C O M f A R I S N O F 



next the tail is globular, and fometimes cylin- 

 drical ; fometimes it is flat, and at other times 

 it is broader than long, &c. With regard to the 

 tail, it is often thicker and fhorter than he re- 

 prefents. The vibratory motion he afcribes to 

 the tail, and by which he alledges the animals 

 are enabled to proceed forward, 1 never could 

 drftingullli in the manner he defcribes. I have 

 feen thefe moving bodies vibrate eight or ten 

 times, from right to left, or from left to right, 

 without advancing the breadth of a fingle hair; 

 and I have obferved many of them which never 

 could proceed forward, becaufe this tail, in place 

 of affifting them to fwim, was, on the contrary, 

 a fmall thread attached to the filaments or muci- 

 laginous part of the liquor, and, of courfe, total- 

 ly prevented the progrefTive motion of the body. 

 Even when the tail appeared to have any mo- 

 tion, it refembled only the fmall bendings of a 

 thread at the end of a vibration. I have feen 

 thefe threads or tails fixed to the filaments, which 

 Leeuwenhoek calls veffels : I have feen them 

 feparate from the filaments, after repeated efforts 

 made by the moving bodies : I have feen them 

 firft long, then diminilh, and at laft difappear. 

 Thus thefe tails ought to be regarded as acci- 

 dental appendages, and not as real members of 

 the moving bodies. But, w4iat is more remark- 

 able, Leeuwenhoek exprefsly affirms, in his let- 

 ter to Lord Brouncker, that, befides the tailed 

 animals, he obferved in this liquor animalcules 

 flill more minute that had no tails, and were 



perfedly 



