204 Proceedings of the Royal Physical Society. 
XX VI.—The Cyst of Amoeba proteus. By Lucy Agnes Carter, 8.N.D., 
B.Sc., Strang Steel Scholar, Glasgow University. 
(With Plate.) 
(Read 22nd February 1915. MS. received 22nd February 1915.) 
INTRODUCTION. 
Work on the various types of amoebz, both free-living and parasitic, 
proceeds apace, and as each life-history reveals itself, the hope that the 
complete life-cycle of one of our largest free-living types, A. proteus, may 
soon be added to the already long and interesting list, increases as the 
smaller species are eliminated from the field. 
The only recorded work on the encystment of A. proteus, available up to 
the present time, is a paper by Scheel, which appeared in the Festschrift 
Carl von Kupffer, 1899. The author preludes his article with a short note 
of the work done by previous writers on reproduction in the amoeba group ; 
this dispenses with the necessity for any such summary here. 
The cyst about to be described corresponds very well in size and out- 
ward appearance to that studied by Scheel, but there are palpable differences. 
Owing to the fact that Scheel has figured no stage of the cyst until the 
secondary nuclei are formed and the young amoebe are about to be cut 
off from the protoplasmic matrix, it is difficult, in face of these differences, 
to decide whether the cysts are the same or not. 
MATERIAL. 
The cysts were found during two successive winters in material supplied 
every second day by Mr T. Bolton of Birmingham, from a pond which for 
three years has yielded no large amoebe other than A. proteus. The 
material used in an earlier paper’! was obtained from the same source. 
Although the amoebz encysted when left undisturbed in the Petri-dishes 
into which the incoming supplies were severally put, they never did so 
when isolated in any kind of artificial culture medium. 
The first appearance of cysts was in February 1912. As some of 
these were already well developed, the amoebze must have encysted much 
earlier ; this was found to be the case the following year. The months 
1 Carter, ‘ Note on a Case of Mitotic Division in A. proteus,” Proc. Roy. Phys. Soc. Hdin., 
vol. xix., No. 4, p. 54, 1918. 
