PREFACE 



THIS book, as its name implies, is intended to serve as an intro- 

 duction to the subject with which it deals, and not in any way as a 

 complete treatise upon it. The science of " protozoology," as it is 

 now generally termed, covers a vast field, and deals with an immense 

 series of organisms infinitely varied in form, structure, and modes of 

 life. In recent years the recognition of the importance of the 

 Protozoa to mankind in various ways, and especially from the 

 medical point of view, has focussed attention upon them, and has 

 brought about a great increase of our knowledge concerning these 

 forms of life. To set forth adequately and in full detail all that is 

 now known about the Protozoa would be a task that could not be 

 attempted in a volume of this size, but would require a work many 

 times larger. 



The aim of the present work is essentially didactic that is to say, 

 it is intended to furnish a guide to those who, having at least some 

 general knowledge of biology, desire a closer acquaintance with the 

 special problems presented by the Protozoa. First and foremost, 

 it attempts to define the position of these organisms in Nature, and 

 to determine, as far as possible, in this way exactly what should be 

 included under the term " Protozoa," and what should be excluded 

 from the group. Secondly, its function is to guide the student 

 through the maze of technicalities necessarily surrounding the study 

 of objects unfamiliar in daily life, and requiring, consequently, a 

 vocabulary more extensive than that of common language ; and 

 with this aim in view, care has been taken to define or explain fully 

 all technical terms, since confusion of thought can be avoided only 

 by a clear understanding of their exact significance and proper 

 application. Thirdly, it aims at introducing the student to the 

 vast series of forms comprised in the Protozoa and their systematic- 

 classification, based on their mutual affinities and inter-relationships, 

 so far as these can be inferred from their structural peculiarities and 

 their life-histories. And, incidentally, attention has been drawn 

 specially to those parts of the subject where the Protozoa throw 



