II 



PHYLUM PROTOZOA 



81 



genus also has stinging -capsules or nematocysts (a, b) in the protoplasm, 

 resembling those of Zoophytes (see Section IV.), and has numerous nuclei of 

 two sizes, distinguished as meganuclci (nu.) and micronuclei (nu'.). In the 

 Adinidce the characteristic groaves are absent. 



1. Cleno dinium 



2.CeraHur> 3-Prorocenrrum 



4.Polykrikos 



FIG. 60. Various forms of Dinoflagellata. 2 shows the shell only ; 4a 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 Butschli's Protozoa.) 



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. 



The Dinoflagellata are mostly marine. Some are phosphorescent. Certain 

 kinds occasionally occur in such abundance in bays and estuaries and in 

 ponds and lakes as to cause a deep brownish or red discoloration of the water. 



ORDER 4. CYSTOFLAGELLATA. 



This group includes only two genera, Noctiluca and Leptodiscus. A 

 description of Noctiluca miliaris, the organism to which the diffused phos- 

 phorescence of the sea is largely 

 due, will serve to give a fair 

 notion of the leading character- 

 istics of the order. 



Noctiluca (Fig. 61) 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 (bg.), noticeable for 

 its transverse striation. Near 

 the base of this flagellum is the 

 mouth (m.), leading into a short 

 gullet in which is a second 

 flagellum (/.), 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. 



VOL. i a 



Fia. 61. Noctimca miliaris. a. the adult 

 animal ; b, c. flagellulse ; bg. tentacle ; /. flagel- 

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



