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might be equally well placed along with these coloured Flagel- 

 lata. There may be more tliaii a single flagellum ; Anisonema, 

 e.g., has two, one of which is stout and used for springing ; 

 others have four or six alike in character. 



20. A remarkable group, the members of which resemble 

 the collar-cells of the sponges in form (§ 8), has represent- 

 atives both in fresh and in salt water. Salpingceca, 

 which has both the collar and a case, may serve as an ex- 

 ample of it. Finally, reference must be made to two forms 

 of marine Flagellata, which are interesting on account of 

 assisting in producing the phosphorescence of the sea, in which 

 they occur in great numbers. Ceratium may be taken as a 

 type of the larger group, marked by the possession of a resist- 

 ent case, and by a second flagellum situated in a groove, which 

 looks like a row of cilia when in movement. Noctiluca, on the 

 other hand, attains a much larger size ; it is peach-shaped, with a 

 tentacle at the head of the groove which lodges the mouth, and 

 a flagellum and tooth within the groove. It is distinguished by 

 the reticular character of the protoplasm within the cuticle. 



"21. As a type of the Infusoria proper or Infusoria Ciliata, one 

 of the largest and commonest forms, Paramoeclum — the slipper- 

 animalcule — found everywhere in water containing decaying or- 

 ganic matter, m ly be studied. It attains the size of l-lOOth of 

 an inch, and is, therefore, visible to the naked eye. Mouth and 

 anus are both present, as they are in all, with the exception of 

 s me parasitic forms (Opalina), and there is a distinct o?soi)hagus 

 leading inwards from the mouth to the endoplasm. The body is 

 uniformly covered with similar cilia (it belongs to the order Holo- 

 tricha) and there are, in addition, certain thread-like structures — 

 " trichocysts " — peculiar to this family, which can be thrust out 

 from the cuticle and seem to have a function similar to that 



