PHYLUM PROTOZOA 



79 



Reproduction is, as usual, by binary fission, the process taking place some- 

 times in a tiro -swimming individual, sometimes in one which has lost its flagella 

 and come to rest. 



Cleno dinium 



2.Cerarium 3.Prorocentrum 



4.Polykrikos 



Fio. 59.;— Various forms of Dinoflapellata. 2 shows the shell only; Art is an undischarged, 

 and b a discharged stinging-capsule ; chr. chromatophores ; jt. 1, longitudinal flagellum ; 

 fl. ?, transverse flagellum ; I. <jr. longitudinal groove ; ntc. nematocyst ; nu. meganucleus ; 

 wit', micronucleus ; pg. pigment spot ; t. gr. transverse groove. (From BUtschli's Protozoa.) 



The Dinoflagellata are mostly marine. Some are phosphorescent. Certain 

 kinds occasionally occur in such abundance in bays and estuaries as to cause a 

 deep brownish or red discoloration of the sea-water. 



Order 4. — Cystoflagellata. 



This gioup includes only two genera, Noctiluca and Leptodiscus. A descrip- 

 tion of Noctiluca miliaria, the organism to which the diffused phosphorescence 



of the sea is largely due, will serve 

 to give a fair notion of the leading 

 characteristics of the order. 



Noctiluca (Fig. 60) is a nearly 

 globular organism, about ^ mm. in 

 diameter. It is covered with a 

 delicate cuticle, and the medullary 

 protoplasm is greatly vacuolated. 

 On one side is a groove from 

 which springs a very large and 

 stout flagellum or tentacle (by.), no- 

 ticeable for its transverse striation. 

 Near the base of this flagellum is 

 the mouth (m. ), leading into a short 

 gullet in which is a second flagel- 

 lum (/. ), very small in proportion 

 to the first. On the side opposite 

 to the mouth is a strongly marked 

 superficial ridge. The light-giving 

 region is the cortical protoplasm. 

 Reproduction takes place by binary fission, the nucleus dividing indirectly. 

 Spore-formation also occurs, sometimes preceded by conjugation, sometimes not. 



Fie. 60. —Noctiluca miliaria, a. the adult 

 animal ; b, c. flagellula; ; !>;i. tentacle ; /. flagel- 

 hun ; m. mouth ; t». nucleus. (From Lang.) 



