Peridiniaceae 67 



side of this 'pusule,' and in a median position, is another smaller spherical 

 'pusule,' which also has a duct leading to the flagellar pore. Schiitt termed 

 this the 'collecting pusule.' Other much smaller 'pusules' are aggregated 

 about the larger ones. Schiitt apparently regarded the canals as ducts for 

 the discharge of the fluid contents of the 'pusules' through the flagellar 

 pore. Kofoid ('09 A) has, however, produced evidence to show that the small 

 'pusules' form on the walls of the main sacs and pass peripherally, 'discharging 

 their contents, perhaps by osmosis, at the surface.' His observations all 

 indicate that the movement of fluid is inwards ' through the flagellar pore 

 into the sack and collecting " pusules," and thence into the daughter and 

 accessory vacuoles, perhaps also into typical plasma vacuoles, and ultimately 

 out through the apical and other pores of the thecal wall.' He also points 

 out that the maximum development of the 'pusule apparatus' occurs in 

 those colourless forms in which the chromatophores are replaced by leuco- 

 plasts, and suggests that perhaps this system of cell-structures is in some 

 way concerned with a saprophytic mode of nutrition such as might occur 

 in zones of decaying plankton. 



THE CHROMATOPHORES AND NUTRITION. In the PeridiniaceaB the chro- 

 matophores are so delicate that they can only be satisfactorily observed 

 in the living organisms or by the most careful fixation and staining. In 

 outward form they vary considerably; in some they are disc shaped, in others 

 rod-like or band-like, and they may be much lobed. The disc-shaped and 

 band-like chromatophores are usually thick in the middle and thin at 

 the margin, and are disposed in a parietal manner. On the other hand, 

 the rod-like chromatophores are usually arranged radially from the periphery 

 inwards. The chromatophores are embedded in the peripheral part of the 

 cytoplasm, but their distribution is by no means uniform in different parts 

 of the cell. In Glenodinium uliginosum, and in the encysted state of 

 Peridiwium anglicum, the cell may contain only one large parietal, lobed 

 chromatophore (G. S. W., '09). In colour they vary from yellow to brown, 

 but in Peridinium herbaceum Schiitt they are green. The usual yellow- 

 brown chromatophores are stated to possess three pigments: phycopyrrin, 

 peridinin, and a peculiar form of chlorophyll, but further investigation of 

 these pigments is desirable before any definite statements can be made 

 concerning them. It is not improbable that the different shades of colour 

 are due to varying proportions of chlorophyll, xanthophyll and carotin, as in 

 the case of Diatoms. The depth of colour varies according to the environ- 

 ment. In some of the freshwater forms the chromatophores are paler in 

 summer than in spring or autumn. 



Some of the Peridiniacese, such as Glenodinium apiculatum, Peridiiiinni 

 achromaticutn, P. Steinii, etc., are destitute of chromatophores. 



52 



