68 Peridiniese 



Nutrition. The great majority of the Peridiniaceas possess chromato- 

 phores and have a typical holophytic nutrition. The colourless forms are 

 mostly saprophytes. An animal-like nutrition has been either observed 

 or suspected to occur in a number of genera and species, even in certain 

 forms which possess definite chromatophores. Both Entz and Schiitt have 

 stated that the ball-like structures found within the cells of certain species 

 of Ceratium, Gonyaulax, Goniodoma, Peridinium, Dinophysis, Oxytoxum, and 

 other genera, are the remains of ingested food-materials, but in no single 

 instance has the actual ingestion been observed. Zacharias found the valves 

 of minute diatoms of the genera Cyclotella and Navicula within the cells of 

 Glenodinium apiculatum, and Schilling has also seen the valves of small 

 diatoms within the protoplast of Glenodinium edax. The natural assumption 

 is that these diatoms were picked up and engulfed as food. There is, how- 

 ever, no proof of this ; neither does it seem probable that an organism com- 

 pletely enveloped in an armature of strong plates, the slightest dislocation 

 of which usually causes its death, is capable of engulfing solid bodies such as 

 diatom-cells. 



The food-reserves are starch and a fatty oil. Starch is found in grains of 

 variable size, which sometimes show a stratification ; it is not confined to the 

 forms which possess chromatophores, but occurs in certain of the colourless 

 species, the grains possibly arising by the activity of leucoplasts. Fatty oil 

 is stored in small globules or as irregular masses. It may accumulate in any 

 part of the cell or be more or less confined to certain regions, and its accumu- 

 lation is brought about by the agency of lipoplasts which are surrounded by 

 a special membrane. 



CELL-DIVISION AND MULTIPLICATION. The multiplication of the Peri- 

 diniacese is effected almost entirely by vegetative cell-division. Such divisions 

 occur mostly during the night, but only under favourable conditions, and 

 generally while the organisms are motile. The plane of division is longi- 

 tudinal in Plialacroma, and obliquely longitudinal in many genera, such 

 as Ceratium. The nucleus first divides, the parallel threads (vide page 64) 

 dividing across the middle, whereupon the whole nucleus constricts into two 

 halves, each of which becomes rounded. In Ceratium, division of the whole 

 protoplast follows immediately after the division of the nucleus, and then the 

 hard cell-wall begins to separate into two pieces along certain of the existing 

 sutures between the plates. Lauterborn ('95) first described this line of 

 separation in Ceratium hirundinella, but Kofoid ('07 C and D) has given a 

 much better account of the fission-plane in a number of other species of the 

 genus (figs. 43 arid 49). 



Starting from the ventral area in the apical half of the cell, the line of 

 fission passes between 4" and 4', 4" and 3', 3" and 3', 3" and 2', 3" and 2"; then 



