63 



umltistriatum Kofoid ('07 B), in which species they occupy a bigger area 

 of the cell-wall than the plates themselves (consult fig. 45). It has been 

 noticed in many species of Peridinium that the intercalary bands are wider 

 and the striations stronger in old than in young cells, and it is probable that 

 this increase in width of the intercalary bands is a means whereby the 

 armour-plated cell may grow in size. Adjacent plates are joined by over- 

 lapping margins, which are often grooved and firmly cemented. It is by an 

 extension of the surface of these thin outer flanges of the plates that the 

 increase in width of the intercalary bands is accomplished. Kofoid ('09 A) 

 states that the increased width of the intercalary bands is associated with 

 the thickening of the cell-wall and the reduction in the porulate areas of the 

 plates, and he suggests that these bands may be structural adaptations 

 facilitating communication between the exterior and the interior of the cell, 



Fig. 45. Peridinium multistriatum Kofoid. Dorsal (left figure) and ventral (right figure) views 

 of cell, showing very wide striated intercalary bands, x 530 (after Kofoid). In both figures 

 the cell-wall is slightly dislocated immediately behind the girdle. 



and increasing the strength of the union between the plates. The striations 

 are oblique structures within the wall or on the oblique faces of the over- 

 lapping margins of the plates. They are most probably of the nature of 

 modified pores or canals, and are sometimes continued beyond the edges 

 of the overlapping margins. 



In some of the marine forms there is an intracellular skeleton consisting 

 of curved rods, five-rayed stars, or perforated basket-like structures (fig. 46 A 

 and B). 



In some part of the longitudinal furrow or of the ventral area there is an 

 aperture through the cell-wall known as the flayellar pore, through which 

 the two flagella pass as they leave the protoplast. This pore may be cleft-like, 

 round, or oval, and its outer margin is sometimes provided with small teeth. 



THE PROTOPLAST. The protoplast is colourless in most forms, but in 

 its outer portion it may be faintly tinged with red. The peripheral region 



