DIV. 



THALLOPHYTA 



387 



(Fig. 318) or the cells have long horn-like processes. These adaptations enable 

 the organisms to remain floating in the water ( 18 ). 



In some Dinoflagellatae the chromatophores are only represented by colourless 

 leucoplasts. Such species live either as saprophytes or in the same way as 

 animals. Spirodinium hyalinum is a colourless, naked, fresh-water form, the 

 protoplast of which for the purpose of absorbing nourishment loses its cilia 

 and assumes the form of an amoeba ; in this condition it encloses and digests, 

 small Algae. 



Some marine Peridineae (e.g. Ceratium tripos, Peridinium divergens) are 

 phosphorescent, and play a considerable part in the phosphorescence of the sea ( 5 ). 



Reproduction is effected by division usually of the motile cells. In certain 

 genera (Peridinium, Cystodinium [Fig. 317]) the motile cells enter into a longer 



FIG. 318. Peridineae of the plankton. A, Ceratocorys horricla var. africana, Indian Ocean (x 250) ; 

 B, Ceratium tripos intermedium var. aequatorialis, Indian Ocean (x 62); C, Ceratium tripos 

 ciU'lterum, and D, Ceratium pal mat urn, Atlantic Ocean (x 62); E, Ceratium furca, Atlantic 

 Ocean (x 125). (After G. KARSTKN.) 



or shorter resting stage and form non-ciliated cysts in which division takes place ; 

 the daughter cells emerge from the swollen cysts as swarm cells. Lastly the 

 motile stage may be completely suppressed and the two naked daughter cells 

 emerge from the swollen cyst as non-ciliated cells provided with their own cell 

 walls (Hypnodinium). 



Some genera (Ceratium} form thick- walled resting-cysts within the old parent 

 membrane. 



Sexual reproduction has not been demonstrated in the Dinoflagellatae ( 19 ). 



CLASS VI 

 Diatomeae (Diatoms) ( ! < n > " 23 ) 



The Diatomeae (Bacillariaceae) constitute a very large class of 

 unicellular Algae. They occur, usually associated together in large 

 numbers, in both fresh and salt water, and also on damp soil. 



