1 86 



THE MASTIGOPHORA 



that the endogenous formation of swarm-spores results in the production 

 of gymnodiniform young. 



Chromatophores, indefinite in number, may be green, reddish yellow, 

 or absent. The reddish-yellow variety of chlorophyll has been named 

 peridiniu (Schiitt). The colour of the chromatophores turns green at 

 death owing to the solubility of the peridinin. Many genera comprise 

 both coloured and colourless species, but the latter are furnished with 

 leucoplasts. Other plastids described as fat-forming bodies or lipoplasts- 

 are also met with. 



The vacuole-system consists of saccules and pusules discharging into 

 the depression from which the Hagella arise. 



The excrescences of the carapace serve as floats for these pelagic 

 organisms and occur as linear (Ceratium, Fig. 11) or foliaceous 



FIG. 11. 



Ceratium tripos. Dorsal view 

 shortly after fission, the two 

 daughter individuals still at- 

 tached to each other. , the 

 anterior individual protected 

 by the greater part of the 

 parent's epitheca ; 6, the pos- 

 terior individual protected by 

 the greater part of the hypo- 

 theca. (After Sohiitt.) 



FIG. 12. 



Peridiniu m divergens. Ventral view 

 .showing the vacuole-system. c.p, the 

 small collector-pusule surrounded by :i 

 rosette of still smaller pusules which 

 open into it; s.p, the large sac-pusule or 

 reservoir ; both opening into the fundus 

 (/), from which both the transverse flagel- 

 lum (0 lying in the annulus (a) and the 

 longitudinal flagellum (/) arise. (After 

 Schiitt.) 



(Ornithocercus, Fig. 10 (8)) expansions. At the anterior or apical end of 

 the cell there is an apical pore which is frequently closed by a perforated 

 plate resembling a madreporic plate (e.g. Blepharocysta}. The sulcus is 

 ventral, but there is no plane of symmetry. 



Some species of Ceratium and Peridinium are found in freshwater 

 lakes, but the other genera appear to be exclusively marine. 



In respect of individual numbers the principal habitat of the Peri- 

 diniaceae is in the cold waters of the North Sea, Baltic, and North 

 Atlantic. In point of specific divergence the southern waters are richer. 

 Individual variation is often excessive, and seasonal dimorphism has also 

 been noted. 



Genera and species are determined by the form of the body and by 

 the characters of the cuirass. 



The Peridiniaceae are divided into four families as follows : 



FAMILY 1. GLENODINIIDAE, intermediate between Gymnodiniaceae and 

 Peridiniaceae. Cuirass soft, membranous, consisting of two structureless- 



