1 88 THE MASTIGOPHORA 



Other genera of Dinophysidae are Phalacrowia, St. ; Dinophysis, Ehrb. ; 

 Histioneis, St. (Fig. 10 (5, 6)), Citharistes, St.; Triposolenia, Kofoid San 

 Diego region of the Pacific. 



SUB-CLASS V. CYSTOFLAGELLATA. 



There are only three genera in this sub-class, and of these 

 Nodiluca has long been known as a widely distributed organism 

 that is often the principal cause of the phosphorescence of the 

 surface of the sea. The other two genera are little known. 



Nodiluca possesses a sub-spherical body with bilateral symmetry, 

 the median plane of symmetry being determined by an elongated 

 groove on the ventral side called the peristome (Fig. 15 (5)), at the 

 bottom of which is the mouth. The nutrition is holozoic, and the 

 rnouth leads directly into the central part of the protoplasm, from 

 whence trabeculae, exhibiting in life a streaming of the granules, 

 radiate outwards towards the periphery. In certain regions the 

 trabeculae are concentrated in the form of dense groups of fibrillae 

 giving rise to a fibrillar plexus. One such plexus arises from the 

 posterior end (/) of the central protoplasm, and is inserted along a 

 thickened linear area of the integument behind the peristome called 

 the bacillary organ, "Staborgan" (Fig. 15 (5, c)). 



The integument consists of a resistent ectoplasm, a dense 

 reticulate layer of alveolar protoplasm. The striated proboscis- 

 like tentacle which arises in the middle line at the anterior end 

 of the peristome, and constitutes one of the most notable features 

 of its organisation, has a length equal to half the diameter of the 

 sphere. It is a flattened contractile organ, convex on its outer side 

 and concave on the inner adoral side. The protoplasmic trabeculae 

 which traverse the tentacle are so disposed as to produce a striated 

 structure comparable to that of striped muscle-fibres. 



Other peristomial organs are the dentiform process; the flagellum, 

 which is borne upon or near a protuberance termed the lip ; and 

 lastly the mouth. The tooth l and the lip are placed asymmetri- 

 cally upon the right wall of the peristome. The mouth occupies 

 the posterior two-thirds of the fundus of the peristome, which is 

 deepest behind and becomes progressively shallower in front. In 

 front of the mouth, that is to say, in the anterior third of the 

 peristome, are the lips, with the flagellum, the tooth, and the 

 tentacle. The flagellum lies well within the peristome and requires 

 practised observation for its discovery. 2 It resembles the typical 

 flagellum of Mastigophora, namely, a filament of uniform thickness 

 from base to apex. The tentacle can be extruded far beyond the 

 confines of the peristome, but it can also be retracted, rolled up, and 

 so escape superficial observation. 



1 The tooth is a protoplasmic organ. 2 It was discovered by Krohn in 1852. 



