74 



ZOOLOGY 



SECT. 



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

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

 and come to rest. 



vctf 



2-Ceratium 3.Prorocenfrum 



4.Polykrikos 



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

 and b a discharged stinging-capsule; chr. chromatophores ; ./?. 1, longitudinal fiagellum ; 

 /'. .'.transverse fiagellum ; I. <ir. longitudinal groove; ntr. iiematocyst ; iiu. meganucleus; 

 /a'/, micronucleus ; p<j. pigment spot ; t. <ji-. transverse groove. (From Biitschli'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, Xortitiica and Leptofllxnix. 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 t< >itfh: (1>f/. ), no- 

 tiecable for its transverse striation. 

 Xcarthe base of this flagellum is 

 the mouth (m. ), leading into a short 

 gullet in which is a second flagel- 

 lum (f. ), 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. .M. Noctiluca miliaris. . the adult 

 animal ; l>, c. fiagellulie ; lt. tentacle ; /. flagel- 

 lum ; HI. mouth ; n. nucleus. (From Lang.) 



