THE 



AMERICAN NATURALIST 



Vol. L. May, 1916 No. 593 



GENERAL BIOLOGY OF THE PROTOZOAN LIFE 



CYCLE 1 



GARY N. CALKINS, Ph.D. 

 Professor of Protozoology in Columbia University 



For five decades after the time of Ehrenberg, the pecu- 

 liar conception of a protozoan as a miniature replica of 

 a metazoan, held by this gifted observer, influenced the 

 study of Protozoa. This influence gradually wore off 

 and, so far as morphology is concerned, ended with the 

 careful observations of Stein, Claparede and Lachmann, 

 Engelmann, Biitschli and Hertwig, who showed that 

 various structures of the protozoan body are not beating 

 hearts, brains, ovaries and stomachs, but are simple dif- 

 ferentiations of the single-celled organisms. 



A more lasting influence of Ehrenberg 's teaching, seen 

 even to-day, is the habit of regarding a single protozoon 

 as the complete expression of a species equivalent to an 

 individual worm, mollusc or mammal. The individual 

 metazoon dies, while the protozoon does not die but grows 

 to full size and divides into two or more— facts which led 

 Weismann to his conclusions regarding mortality in 

 Metazoa and immortality in Protozoa. 



"We owe to Maupas the credit for dissipating this last 

 reminiscence of Ehrenberg 's teaching, and for showing 

 that the single cell is not the final representative of a pro- 

 tozoon species. We are accustomed to the idea that many 



i Opening address Subsection E, Protozoology, Section VIII 2nd Pan- 

 257 



