Xli INTRODUCtORY OBSERVATIOlSrS, 



briflles. No lefs fmgular is the variety of mo- 

 tion peculiar to each. Several fpecies fwim with 

 the velocity of an arrow ; the eye can hardly fol- 

 low them. Some drag the unwieldy body along 

 by painful exertion, and others feem to perfift in 

 perpetual reft. An animalcule will revolve on its 

 centre as the axis of motion, or the anterior part 

 or head is made that axis by another. Some 

 move by undulations, by leaps, or inceflant gyra- 

 tion. In fhort, there is no kind of animal mo- 

 tion, or any other mode of progreffion, that is not 

 pradifed by animalcula. The manner in which 

 they propagate is as remarkable. In general, 

 they produce eggs, many, a living foetus, and 

 others, like a few of the larger animals, both ; 

 fome multiply by a part of the body detaching 

 and becoming a new animal ; fome by a tranf- 

 verfe or longitudinal divifion of the body, and 

 others, by the mother burfting to allow her off- 

 fpring to come into the world. 



Compared with the reft of animated nature, 

 the number of infufion animalcula furpaffes all 

 belief: they are furely the moft numerous. Next 

 are worms, infeds, or fifties ; amphibia and for- 

 pents, birds, quadrupeds ; and laft:, is man. The 

 fpace he occupies on earth is fmall, and the pro- 

 pagation of his fpecies goes flowly on. The hu- 

 fP^n femak produces only pne at a time, that 



after 



