ENCYSTATION OF AOTINOSPHERIUM EICHHORNI. 407 
A few Observations on the Encystation of 
Actinospherium eichhorni under different 
conditions of Temperature. 
By 
Doris L. Mackinnon, B.Se., 
Carnegie Scholar, 1906-1907. 
With Plate 24 and 1 Text-figure. 
Previous to Richard Hertwig’s exact study “Uber Kern- 
teilung, Richtungs-Korperbildung und Befruchtung von 
Actinosphaerium eichhorni” (1898), our knowledge of 
the life-cycle in this heliozoon was still very incomplete. 
Hertwig’s work laid clear for the first time the complicated 
series of changes that take place within the Actinospherium 
cyst, and his subsequent work, Uber Physiologiche Degenera- 
tion bei Actinosphaerium eichhorni” (1904), threw 
further light on the conditions affecting the lfe-processes in 
this organism, both free-swimming and encysted. 
In the last few years cytologists have found in Actino- 
spherium a highly favourable object for experimental cell- 
study. Mr. Geoffrey Smith, of New College, Oxford, working 
in Munich in 1902, made interesting comparisons between 
cultures brought to encyst at different temperatures. While 
in Professor Hertwig’s laboratory in Munich, early in 1907, I 
undertook, at his suggestion, a series of similar experiments, 
to determine, if possible more exactly than previous results 
