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. 



(/) 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. 



( I ) Review of Literature. 



The history of the work already done on the cytology of 

 the Cyanophyceae 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. 



