THE MASTIGOPHORA 



277 



a, 



The transverse flagellum executes undulating movements whicti 

 were formerly mistaken for those of a ring of cilia ; hence the name 

 Cilioflagellata formerly applied to this group. 



The cuirass, composed of cellulose or an allied substance, is in its 

 typical form a perfectly rigid structure, and is 

 often prol mged into spikes and processes which 

 cause the body as a whole to assume strange or 

 even monstrous forms (Fig. 121). Detailed 

 studies on the skeleton have been published by 

 Kofoid in a series of memoirs (374-383). The 

 nutrition is for the most part holophytic, but 

 in some species ingestion of solid food has been 

 observed. A great many parasitic forms have 

 been made known of recent years (Chatton, 

 366-369 ; Caullery, 364) ; these are for the most 

 part forms which, in the vegetative, parasitic 

 phase are inert bodies with no sign of locomotor 

 organs, often fixed and pedunculate when ecto- 

 parasitic ; but in their reproductive phases 

 they betray their affinities by the formation 

 of numerous flagellated swarm-spores exhibiting 

 the typical Dino flagellate structure. 



The pelagic species generally possess chroma- 

 tophores, and frequently a red stigma, which in 

 some genera Pouchetia (Fig. 31), Erythropsis is modified into an 

 eye-like organ. The deep-sea forms, on the other hand, are colourless. 



In many Dinoflagellates a peculiar system of vacuoles is found (Fig. 122), 

 consisting of two sacs containing watery fluid, each of which empties itself 



to the exterior by its own duct. They differ from 

 ordinary contractile vacuoles in possessing a dis- 

 tinct envelope and in not performing rhythmical 

 contractions, and have hence been given the 

 special name of " pusules " (Schiitt). One of these 

 organs, termed the "collecting-pusule," consists of 

 a reservoir-vacuole surrounded by a ring of smaller 

 vacuoles which emptv themselves into it ; the 

 other, termed the " sack-pusule," is a large cavity 

 which takes up a great part of the interior of the 

 cuirass. The function of these organs is probably 

 hydrostatic. 



The commonest method of reproduction is 

 binary fission in the transverse plane of the body, 

 in which each daughter-individual receives a half 

 of the cuirass of the parent and regenerates the 

 half that is wanting. Fission rapidly repeated may 

 lead to the formation of chains of individuals. In 



other cases multiple fission within the cuirass has been observed, leading to the 

 formation of swarm-spores which are possibly gametes ; but little is known of 

 the sexual processes of these organisms. 



The Dinoflagellates are an exceedingly abundant and widespread group, 



FIG. 120. Glenodi- 

 niiim cinctum, 

 Ehrenberg. a, 

 Amyloid granules ; 

 b, stigma ; c, chro- 

 matophores; d, 

 flagellum of the 

 transverse groove ; 

 e, flagellum of the 

 vertical groove ; v., 

 vacuole. From 

 Lankester. 



FIG. 121. Ceratocorys 

 horrida: cuirass. After 

 Stein, from Lankester. 



