Vol. 8, 1922 
ZOOLOGY: M. BUNTING 
299 
The time periods occupied by the different stages in the Hfe cycle at 
room temperature, as a rule, have been the following : — The cyst lives in a 
proper medium indefinitely. When cysts are planted on fresh media, 
amoebae may emerge in two or three hours and remain active from three 
to four days, rarely longer, and then encyst. The Tetramitus may ap- 
pear in ten to twelve hours after transplantation of the cysts, continue 
numerous for two days and gradually disappear the third day as these 
become transformed into amoebae or die. 
Exceptions to the above have occurred in two cultures in which activ- 
ity of Tetramitus lasted for about a month. The study of the living 
animals together with the cytological examination of fixed and stained 
specimens from each culture revealed an increase in the number of nuclei 
to two, three and four, also the presence of giants and a greater proportion 
of animals of irregular shape. 
While great numbers of these flagellates have been under observation for 
more than a year, no stages in the life history have been observed other 
than those described above. Binary fission for Tetramitus has been 
noted by Perty,^ Dallinger and Drysdale,^^ Stein,^^ Klebs,^^ and Alexeieff.^^ 
Although no sexual stages nor spore formation such as described by Dal- 
linger and Drysdale have been observed in these studies, nevertheless these 
observers did see the flagellate become partly amoeboid and a longer ob- 
servation should have revealed to them the complete change to an 
amoeba. 
In a life cycle of this kind, in the absence of sexual phenomena it is 
uncertain whether the amoeboid or the flagellate phase should be consid- 
ered as the adult or dominant one, especially since non-sexual reproduction 
is extensive in both phases. A thorough study of the life cycles of other 
"amoebae" and other "flagellates" might reveal further examples of trans- 
formations of the kind here described. 
In closing I wish to express my great indebtedness to Doctor D. H. Wen- 
rich who has been ever ready to aid this investigation by participation and 
by fruitful suggestions. Also for the continued interest and aid of Pro- 
fessor Clarence H- McClung who has helped to surmount the many diffi- 
culties encountered and who, with the Graduate School of the University 
of Pennsylvania, has provided the facilities of the Zoological Laboratory 
for this research. 
1 Perty, M., Zur Kenntniss Kleinster Lebensformen . 1852. 
2 Whitmore, E. R., Archiv. ProHstenk., 23, 1911 (81-95). 
3 Kofoid. C. A.. Sci. N. S., 42, 1915 (937-940). 
* Wilson, C. W., Univ. Gal. Puhl. Zodl., 16, 1915-1917 (241-292). 
5 Pascher, A., Archiv. Protistenk., 38, 1917 (1-87). 
® Dobell, C, and O'Connor, F. W., The Intestinal Protozoa of Man. London, 1912. 
^ Sellards, A. W., Philip. J. Sci. (Ser. B), 6, 1911 (281-298). 
