56 



Peridin&x 



protoplasm. Blackmail ('02) has shown that dilute acetic acid and also 

 absolute alcohol will so raise the irritability of the protoplasm that the 

 organisms react more vigorously to the stimulus of shaking and thus glow 

 with a brighter light. 



Fig. 40. A, Pyrocystis pscudonoctiluca Wyv. Thorns., a normal uncontracted specimen after 

 treatment with osmic acid, x 150; B and C, Diplodinium lunula (Schtitt) Klebs ( = Pyrocystis 

 lunula Schiitt), showing flagellated spores of the Gymnodinium-type, x 475 ; D, Pyrocystis 

 fusiformis Wyv. Thorns., a slightly contracted specimen, x 75. (4 and D after Blackman; 

 B and C, after Schiitt). 



Each individual is furnished with a strong wall of cellulose, about 5 /A 

 in thickness (Blackman, '02), which was at first erroneously regarded as 

 siliceous owing to its glassy appearance. The nucleus is large and may 

 be centrally placed, as in the elongated Pyrocystis fusiformis Wyv. Thorns., 

 or laterally situated, as in the spherical P. pseudonoctiluca Wyv. Thorns., but 



