138 AN INTRODUCTION TO ZOOLOGY. 



temporary case of conjugation. The typical Flagellata 

 seems to have something like a mouth ; at least, the 

 entrance of food is confined to one special region. 

 The largest kind belonging to this group is the 

 brightly phosphorescent Nodiluca (night-glow), which 

 is found in the English seas. It has a thick appendage 

 or tentacle, a mouth, which is guarded by a tooth-like 

 prominence, and a vibratile flagellum. 



The Gregarinidce form a group of. the Protozoa 

 which is usually placed near the above. They are 

 parasitic animals; are long in shape, and sometimes 

 have an anterior portion differentiated off from the 

 main cell, which serves to fix the organism to its 

 host, and gives it a false appearance of being bicel- 

 lular. After conjugation, the Gregarine encysts, and 

 forms oval spores provided with a hard case, which 

 are called pseudonavicellce, from their shape, which 

 resembles that of the diatom Navicula (one of the 

 Algce., or simplest forms of plant). When these are 

 ripe, the cyst bursts and lets them out : then each 

 breaks its envelope as a myxopod, i.e. amcebiform cell. 



The Oiliatot have not only a mouth, but also an anal 

 region, for the expulsion of undigested particles. 

 They have a nucleus with a. conspicuous nucleolus, 

 which was described, before its true nature was under- 

 stood, under the name, of Paranucleus ; this latter 

 undergoes conspicuous changes during the process 

 of multiplication, and is to be considered comparable 

 in a measure with the nucleolus of other growing cells 

 (p. 20). 



