





\ ft 5 





BIOLOGY OF THE PROTOZOA. 



CHAPTER I. 

 INTRODUCTION. 



A protozoon is a minute animal organism, usually consisting of 

 a single cell, which reproduces its like by division, by budding, or 

 by spore formation and whose protoplasm has passed, or will pass, 

 through various phases of vitality collectively known as the life 

 cycle. 



The maze of microscopic life to which the scientific world was 

 first introduced by Anton von Leeuwenhoek in 1075 included a 

 heterogeneous collection of animals and plants. Crustacea, rotifers, 

 minute worms, diatoms and desmids, as well as the more minute 

 Protozoa, were all grouped together during the eighteenth and nine- 

 teenth centuries, first under the nondescript term animalcula and 

 later under the more ecological term Infusionsthiere of Ledenmiiller 

 (1763). The correct zoological position of the higher types was 

 recognized before the middle of the nineteenth century and the 

 group of strictly unicellular forms was first definitely outlined by 

 von Siebold in 1848 under the name Protozoa, a term substituted 

 by Goldfuss (1820) for Oken's suggestive Urthiere (1805), while the 

 old name Infusoria has been retained for one of the subdivisions of 

 the group. 



The haziness in classification of the older zoologists has not 

 entirely disappeared in the light of modern knowledge and we are 

 confronted today by the difficulties of distinguishing between 

 Bacteria, unicellular Algae and unicellular animals or Protozoa. 

 It is no reflection on modern science that we are unable clearly to 

 differentiate between these three groups. To accept the problem 

 as insoluble at the present time is merely to admit and apply our 

 conviction that evolution is now, and has been in the past, the pri- 

 mary biological principle underlying the diversities of forms and 

 functions of living things. Few biologists today will refuse to 

 accept the view that higher types of animals — Metazoa— have been 

 derived from forms in the past which were more or less similar to 

 present-day Protozoa; or the view that higher plants have been 

 evolved from unicellular plants. The variations and adaptations 



