INTRODUCTION 5 



are devoted to the structural and functional adaptations of the organ- 

 isms in each class. The last three chapters, finally, deal with the rela- 

 tions of the Protozoa to more general problems. 



A. HISTORICAL REVIEW 



The Dutch microscopist, Anton von Leeuwenhoek (1632-1723), 

 using crude lenses of his own make, was one of the first to apply the 

 microscope to scientific investigation. His contributions to micro- 

 scopic anatomy and to physiology, inaugurating as they did the 

 invaluable services of the microscope in biological research, marked 

 an epoch in the history of science. An ardent follower of Harvey, 

 he was one of the first to offer experimental evidence against the 

 current belief that many of the lower organisms arise by spontaneous 

 generation, and on every occasion he sought to establish the truth of 

 Harvey's' dictum ex ovo ornnia. In 1675, while searching for evi- 

 dence of spontaneous generation, Leeuwenhoek discovered " living 

 creatures in Rain water, which had stood but four days in a new 

 earthen pot, glased blew within." 



"This invited me," he continues, "to view this water with great attention, espe- 

 cially those little animals appearing to me ten thousand times less than those repre- 

 sented by Mons. Swamerdam, and by him called Water-fleas or Water-lice, which 

 may be perceived in the water with the naked eye. The first sort by me discovered 

 in the said water, I divers times observed to consist of 5, 6, 7, or 8 clear globuls, 

 without being able to discern any film that held them together, or contained them. 

 When these animalcula or living Atoms did move, they put forth two little horns, 

 continually moving themselves. The place between these two horns was flat, though 

 the rest of the body was roundish, sharp'ning a little towards the end, where they 

 had a tayl, near four times the length of the whole body, of the thickness (by my 

 Microscope) of a SpiderVweb ; at the end of which appear'd a globul, of the bigness 

 of one of those which made up the body ; which tayl I could not perceive, even in 

 very clear water, to be mov ? d by them. These little creatures, if they chanced to 

 light upon the least filament or string, or other such particle, of which there are many 

 in water, especially after it hath stood some days, they stook entangled therein, 

 extending their body in a long round, and striving to dis-intangle their tayl ; whereby 

 it came to pass, that their whole body lept back towards the globul of the tayl, which 

 then rolled together Serpent-like, and after the manner of Copper or Iron-wire that 

 having been wound about a stick, and unwound again, retains those windings and 

 turnings. This motion of extension and contraction continued awhile ; and I have 

 seen several hundreds of these poor little ' creatures, within the space of a grain of 

 gross sand, lye clustered together in a few filaments." * 



This is the first description of a protozoon; and although the descrip- 

 tion is incomplete, it undoubtedly refers to a species of Vorticella. 

 Leeuwenhoek observed several other forms at the same time, but 

 for the most part their identity is uncertain. 



1 See Phil. Trans., London, Vol. XII., 1677, p. 821. 



