240 Phillips on a Comparative Study of the 
of the investigation, has verified the results and has made 
helpful suggestions from time to time. 
The following sections make up the remaining part of 
this paper : 
(1) Review of Literature, p. 240. 
(2) General Morphology of Types Studied, p. 273. 
(a) Material used, p. 274. 
(b) Methods employed, p. 275. 
(c) The cell wall and sheath, p. 279. 
(d) The central body, p. 282. 
(e) The chromatophore, p. 289. 
(f) The granules, p. 292. 
(g) Vacuoles, p. 294. 
(h) Other cell-constituents, p. 294. 
(3) Morphology of the Dividing Cell, p. 295. 
(4) Protoplasmic Continuity, p. 299. 
(5) The Heterocyst, p. 301. 
(6) Spore Formation, p. 302. 
(7) Motility, p. 307. 
(8) Main conclusions, p. 323. 
(9) General summary of results, p. 325. 
(10) Bibliography, p. 327. 
(11) Explanation of Plates XXIII, XXIV, XXV, p. 332. 
(1) Review oF LITERATURE. 
The history of the work already done on the cytology of 
the Cyanophycez is one of conflicting opinion. The exist- 
ence of a nucleus, for example, has been affirmed in the 
strongest terms by careful investigators, backed by seem- 
ingly conclusive experiments, only to be retracted later. 
Such views have been attacked by other equally capable 
workers, who as strongly denied the existence of a nucleus, 
and fortified their conclusions by apparently good evidence, 
sometimes even with the identical experiments used by the 
exponents of the nuclear theory. 
