PROTOZOA. 



D. — Predominantly Active Forms (ciliate and flagellate), 

 generally called Infusorians. 



(Occurring in fresh or sea water, abundant in infusions. ) 



9. Flagellata, units with a definite rind, with one or a few actively 

 undulating locomotor processes (flagella), often with a distinct aperture 

 for the entrance of food. Reproduction by division into two, or by 

 multiple division within a cyst. Conjugation and encystation are 

 common. Some forms are colonial, and suggest the transition to 

 Metazoa. 



Examples. — Mastigamoeba, possessing a flagellum and amoeboid pro- 

 cesses ; Euglena, with green or variable colouring matter, probably 

 feeding for the most part like a plant ; Volvox, also green, forming 

 colonies, which illustrate the beginning of sex ; Codosiga, with stalked 

 colonies, each individual with a collar around the base of the flagellum ; 

 Proterospongia, colonial, like a detached piece of sponge. 



10. DlNOFLAGELLATA, very successful Protozoa, which combine 

 activity and passivity, having two flagella and generally a cellulose 

 coat. The one flagellum projects from a longitudinal groove, the other 

 lies in a transverse groove. Mostly marine. 



Examples. — Peridinium and Ceratium. 



n. Rhynchoflageli.ata, large forms, with firm skin and very 

 spongy protoplasm, with two flagella, the larger one striated like a 

 muscle, springing from a deep groove, the smaller one near the aperture 

 for the food. 



Examples. — The phosphorescent Noctiluca ; Leptodisctis medusoides, 

 disc-like in form, swimming like a miniature medusoid. 



12. CiLiATA, provided with numerous bending processes or cilia, 

 which drive the animals swiftly, and waft food-ijarticles into the 

 "mouth." There is a definite rind. Beside the large macro-nucleus 

 there always lies a micro-nucleus or "para-nucleus." There are 

 usually two contractile vacuoles. Multiplication by rapidly succeeding 

 divisions ; in rare cases spores seem to be formed. Conjugation (essential 

 to the vitality of the species) has in some cases at least been shown to 

 be associated with intimate interchange of para-nuclear material. Para- 

 sitic forms, some mouthless, are not uncomrnon. 



Examples. — {a) Peritricha, with a circle of cilia at one end or at 

 both, e.g., Vorticella. (b) Heterotricha, with long and short cilia, e.g., 

 Stentor ; Balantidium coli, in intestine of man. (c) Holotricha, uni- 

 formly ciliated, e.g., Paramecium; Opalina, in intestine of frog, with 

 numerous nuclei, and no contractile vacuoles, (d) Hypotricha, locomotor 

 cilia confined to under surface, e.g. , Stylonichia. 



13. AciNETARiA, ciliated when young, and probably derived irom the 

 Ciliata, but more passive when adult. They are fixed in adult life, 

 generally stalked, and bear tentacle-like processes often suctorial. The 

 nucleus is sometimes branched. They have one or more contractile 

 vacuoles. They multiply by division, or by the formation of buds which 

 usually remain for a time partly enclosed by the parent. Their food 

 consists of other Protozoa. They represent "an extreme modification 



