PHYLUM PROTOZOA 



79 



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

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

 and come to rest. 



Clenodinium 



2.Cerahiam S.Prorocenlrum 



4.Polykrikos 



Fig. 59.— Vai-ious foi-ms of Dinofla^ellata. 2 shows the shell only ; Ua is an undischarged, 

 and b a discharged stinging-capsule ; clir. chromatophores ; Jl. 1, longitudinal iiagellum ; 

 /. ^, transverse flagellum ; I. gr. longitudinal groove; ntc. nematocyst ; nv. meganucleus ; 

 «u'. niicronucleus ; 'pij. pigment spot ; t. gr. transverse gi'oove. (From Btitschli's Protozoa.) 



The Dinoflagellata are mostly marine. Some are phosphorescent. Certain 

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

 deep brownish or red discoloration of the sea-water. 



Order 4. — Cystoflagellata. 



This group includes only two genera, Nocliluca 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. CO) 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 ttntaiie (hg. ), no- 

 ticeable for its transverse striation. 

 Near the base of this flagellum is 

 the mouth (m.), leadinginto 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. 



Fig. 60. —Noctiluca miliaris. a. the adult 

 animal ; h, c. flagellulse ; hg. tentacle ; /. flagel- 

 lum ; 1,1. mouth ; n. nucleus. (Fi-om Lang.) 



