46 PROTOZOA 



the largest nuniber of species to the roll. Ehrenberg about 1840 

 described, indeed, an enormous nuniber of forms with much care, 

 and in detail far too elaborate for the powers of the microscope 

 of that date : so that he was led into errors, many and grave, 

 which he never admitted down to the close of a long and honoured 

 life. Max Schultze did much good work on the Protozoa, as well 

 as on the tissues of the JVIetazoa, and largely advanced our con- 

 ceptions of protoplasm. His work was continued in Germany by 

 Ernst Haeckel, who systematised our knowledge of the Eadiolaria, 

 Greeff, Eichard Hertwig, Fritz Schaudinn, and especially Biitschli, 

 who contributed to Bronn's Thier-Rcicli a monograph of monu- 

 mental conception and scope, and of admirable execvition, on 

 which we have freely drawn. Cienkowsky, a Eussian, and James- 

 Clark and Leidy, both Americans, have made contributions of 

 high quality. 



Lankester's article in the Emydoixvdia Britannica was of 

 epoch-making quality in its philosophical breadth of thought. 



Delage and Herouard have given a full account of the Protozoa 

 in their TraiU de Zoologie ConcrHe, vol. i. (1896) ; and A. Lang's 

 monograph in his Vergleichende Anatomic, 2nd ed. (1901), contains 

 an admirable analysis of their general structure, habits, and life- 

 cycles, together with fall descriptions of well- selected types. 

 Calkins has monographed "The Protozoa" in the Columbia 

 University Biological series (1901). These works of Biitschli, 

 Delage, Lang, and Calkins contain full bibliographies. Dotlein 

 has published a. most valuable systematic review of the Protozoa 

 parasitic on animals under the title Die Protozoen ah Parasiten 

 %nd Krankheitserreger (1901); and Schaudinn's Archiv filr 

 Protistenkunde, commenced only four years ago, already forms 

 an indispensable collection of facts and views. 



The protoplasm of the Protozoa (see p. 5 f.) varies greatly in 

 consistency and in differentiation. Its outer layer may be 

 granular and scarcely altered in Proteomyxa, the true Myxo- 

 mycetes, Filosa, Heliozoa, Eadiolaria, Foraminifera, etc. ; it 

 is clear and glassy in the Lol)ose Eliizopods and the Acrasieae ; 

 it is continuous with a firm but delicate superficial pellicle of 

 niembraiious character in most Flagellates and Infusoria ; and this 

 pellicle may ag;iin be consolidated and locally thickened in some 

 members of both groups so as to form a coat of mail, even with 

 definite spines and hardened polygonal plates (Colcps, Fig. 54, 



