16 ESSENTIALS OF ZOOLOGY 



from the conjugation divides successively to form eight nuclei. 

 Seven of these are macronuclei and the eighth divides to form 

 the corresponding micronuclei, when the seven individuals 



Fission Formation of microzooids Conjugation 



FIG. 7. Reproduction of Vorticella. The diagrams illustrate fission, the 

 formation of the microzooids, and the fusion of a microzooid with a stalked 

 Vorticella. 



separate and commence a fresh series of ordinary divisions. 

 But reconstruction after conjugation is variable, even in the 

 same species. 



Colonial forms allied to Vorticella are also common. They 

 result from longitudinal fission involving a part of the stalk, 

 the individuals remaining together, e.g. Epistylis, Carchesium, 

 Zoothamnium. Such colonial vorticellids will be found to be 

 very common. 



Many flagellate Protozoa, usually called monads, will have 

 been seen by the student while looking for the types described 

 above. They illustrate another modification of the individual 

 cell and are nearly always very small. Almost any of these free 

 forms will show the active spiral movements produced by the 

 one or the two whip-like processes with which the simple cell 

 is furnished. The contractile processes are called flagella, and 

 usually spring from one pole of the cell. The protoplasmic 

 body is very simple, consisting of cytoplasm containing a 

 single nucleus, vacuoles, and frequently a contractile vacuole. 

 The ectoplasm is very thin. Of these Flagellata some are 

 plants, some animals, and some are to be regarded as protists, 

 while others may be stages in the life-history of Flagellata 

 and other Protozoa. CEECOMONAS is interesting, for it 

 may become lobed posteriorly by amoeboid extension of the 

 cytoplasm. This organism is common in fresh water and in 



