CHAPTER VL 



SPECIAL MORPHOLOGY AND TAXONOMY OF THE 

 MASTIGOPHORA. 



The Protozoa are usually grouped as a phylum of the animal 

 kingdom, notwithstanding the fact that many of them are much 

 more plant-like than like animals. They have also been regarded, 

 quite generally, as the "lowest" types of animals from which the 

 Metazoa have been evolved, various classical theories by Haeckel, 

 Lankester, Biitschli and Metschnikoft" attempting to trace back the 

 metazoon gastrula to prototypes amongst the colonial flagellates 

 many of which are much more closely related to the higher plants 

 than to Metazoa (e. g., Volvo.r, Sytmra, (Ionium, etc.). It is quite 

 conceivable, as Franz (1919) has pointed out, that such theorists 

 have started with a fundamentally wrong assumption and that all 

 Protozoa, instead of being primitive, have been derived from 

 higher plants or animals. The latter point of view, which falls 

 in line with the startling suggestion elaborated in Bateson's presi- 

 dential address of 1914 has much to recommend it, although much 

 might be said against it. It is useful at any rate, if only to challenge 

 the easy assurance so evident in most general zoological text-books, 

 that Protozoa are primitive animals and that Metazoa have been 

 derived in direct line from them. 



Protozoa, primarily, are single-celled organisms which, together 

 with bacteria and the single-celled plants, comprise the group to 

 which Haeckel's term Protista (1868) has been applied. Protista, 

 or even Protozoa, as Newman (1924) has suggested, may well be 

 regarded as a separate kingdom of living things with many charac- 

 teristic features of the plant kingdom on the one side, and of the 

 animal kingdom on the other. It includes the phylum Bacteria, 

 many of the Protophyta, and the phylum Protozoa, each with 

 indefinite boundaries. Of these the Protozoa alone are essentially 

 animal-like, but, through the chlorophyll-bearing forms they inter- 

 digitate closely with the Protophyta, and through the Spirochsetida 

 with the Bacteria. 



CLASSIFICATION OF THE PHYLUM PROTOZOA. 



The inadequacy of any formal statement to convey an idea of 

 the range of forms, structures and activities of the Protozoa is recog- 



