CHLOROPHYCEJE 179 



lives in the tissues of Sarcophyllia, have been insuffi- 

 ciently studied, and probably are identical with 

 Chlorocystis. In Chlorocystis the zoospores.(or gametes) 

 leave the mother-cell without any mucilaginous 

 envelope. No gametes are known in Halosphccra, 

 and zoospores are formed after the division of the 

 nucleus into numerous nuclei. Round these nuclei 

 the protoplasm and chromatophores assemble and 

 form plano-convex bodies, each of which divides by 

 constriction into two zoospores. These are conical in 

 shape, with a slight protoplasmic projection at the 

 base, from which the two cilia arise. Characium has 

 zoospores showing difference of size, but all with two 

 cilia, and these escape by an apical opening of the 

 cell. In Sykidion the zoospores are all of the same 

 size, but before their formation the cell-contents are 

 enclosed within a new membrane. Codiolum has 

 zoospores with two cilia, and also motionless spores. 



The Geographical Distribution of marine Proto- 

 coccacccu is very imperfectly known. All the genera 

 occur in British seas, except a doubtful genus, 

 Plcurocapsa, recorded from the Adriatic. Nearly all 

 the marine forms are known only in European waters, 

 except Chlorocystis Sarcophyci, which is Australian. 

 The pelagic forms are widely distributed, but too 

 little known to permit of a definite statement. 



PLEUROCOCCACE.E. 



General Characters. This order, like its allies, 

 is more largely represented in fresh-waters than in 



N 2 



