114 PROTOZOA 



Coccolithophoridae, a family of Chrysomonadaceae, is strengthened 

 by embedded calcareous spicules (" coccoliths," " cyatholiths," 

 " rhabdoliths "), which in the most complex forms (cyatholiths) 

 are like a shirt-stud, traversed by a tube passing through the 

 stem and opening at both ends. These organisms ^ constitute a 

 large proportion of the plankton ; the spicules isolated, or in their 

 original state of aggregation (" coccospheres," " rhabdospheres "), 

 enter largely into the composition of deep-sea calcareous oozes. 

 They occur fossil from Cambrian times (Potsdam sandstone of 

 Michigan and Canada), and are in some strata extremely 

 abundant, 800,000 occurring to the mm. cube in an Eocene marl. 



The Silicoflagellates have siliceous skeletons resembling that 

 of many Rculiolaria, to which they were referred until the living 

 organism was described (see pp. 79, 86 f). 



The flagellum has been shown by Fischer to have one of two 

 forms : either it is whip-like, the stick, alone visible in the fresh 

 specimen, being seen when stained to be continued into a long 

 lash, hitherto invisible ; or the whole length is fringed with 

 fine ciliiform lateral outgrowths. If single it is almost always 

 protruded as a tugging organ (" tractellum ") ; ^ the chief 

 exceptions are the Craspedomonads, where it is posterior and 

 acts as a scull (" pulsellum"), and some Dinoflagellates, where 

 it is reversible in action or posterior. In addition to the anterior 

 flagellum there may be one or more posterior ones, which trail 

 behind as sense organs, or may anchor the cell by their tips. 

 Dallingeria has two of these, and Bodo saltans a single anterior 

 anchoring lash, by which they spring up and down against the 

 organic debris among which they live, and disintegrate it. The 

 numerous similar long flagella of the Trichonymphidae afford a 

 transition in the genus Pyrsonympha to the short abundant cilia 

 of Opalina, usually referred to the Ciliate Infusoria. 



^ For a full monograph of tliis family see H, Lolimann, in Arch. f. Frotisten- 

 Icwiide, vol. i. 1902, ji. 89. 



^ Delage has well exjjlained the action of the single anterior flagellum which 

 waves in a continuous spiral like a loaded string whirled round one's head ; it 

 thus induces a movement of the water, beyond its actual range, backwards and 

 outwards, maintained by a constant influx from behind, which carries the cell 

 onward at the same time that it necessarily rotates round its axis. If there is 

 a pair of symmetrically placed flagella they co-operate like the arms of a swimmer ; 

 when the second flagellum is unilateral the motion is most erratic, as seen in Iho 

 Bodonidae (and the zoospores of many Chytridieae, which have most of the 

 characters of the Flagellates, though habitually removed to the Fungi). 



