ZOOLOGY 



SECT. 



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. 



C le n o d inium 



S.Cerahum 3.Prorocenlrum 



4.Polykrikos 



Fio. 53. Various forms of Dinoflaerellata. 2 shows the shell only; kn is- an undischarged, 

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

 fl. 2, transverse flagellum ; 1. gr. longitudinal groove ; ntc. nematocyst ; nu. meganucleus ; 

 nu'. micronucleus ; pg. pigment spot ; t. gr. transverse groove, (From Blitschli'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 group includes only two genera, yoctiluca and Leptodiscus. A descrip- 

 tion of Noctiluca miliaris, 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. 54) 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. ), 110- 

 tiecable 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 



animal ; b, c. flagellulse ; b t/ . tentacle ; /. flagel- to the mouth is a strongly marked 



luiu ; m. mouth ; n. nucleus. (From Lang.) 



IK. M. Noctiluca miliaris. 



adult 



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. 



