II 



PHYLUM PROTOZOA 



51 



takes place between one of the former and one of the latter. In 

 Paramceba, which is amoeboid in the adult condition and multiplies 

 by binary fission, when encystation takes place the contents of the 

 cyst become divided up to form flagellulce, each provided with two 

 flagella. These are not known to copulate, but multiply by binary 

 fission and pass directly into the adult amoeboid form, the flagella 

 being lost. In Trichosphcerium (Fig. 33) there is an alternation of 

 generations one generation (1, 2) reproducing by fission and 

 gemmation and then breaking up into amoeboid spores (3) which do 

 not copulate but develop (4) directly into the second generation (), 

 and this after reproducing by fission and gemmation (6'), becomes 

 resolved into bi-flagellate gametes (7, <$'), which copulate in pairs with 

 other similar gametes (.9, 10, 11), the zygotes developing into the first 



FIG. "4. Microgromia socialis. A, entire colony ; B, single zookl ; C, zooid which 

 has undergone binary fission, with one of the daughter-cells creeping out of the shell ; 

 D, flagellula ; c. vac. contractile vacuole ; nu. nucleus ; sh. shell. (From Biitschli's 

 Protozoa, after Hertwig and Lesser.) 



generation (!-}. In some cases copulation takes place, not between 

 specially produced gametes, but between adults ; this is usually 

 followed either by more active multiplication or by passing into a 

 motionless resting condition. A modification of copulation termed 

 autogamy occurs in Amoeba coli (as in a number of Protozoa of other 

 classes). In autogamy the Protozoan divides into two : each of the 

 two nuclei throws off a part of its substance and then unites with 

 the other. 



Most of the Lobosa are free ; some occurring in fresh water, 

 others in the soil, others in the sea. But a number are parasites 

 in the bodies of higher animals. About six species of Amoeba are 

 known to occur as parasites in man, of which number, one Amoeba 

 (Entamoeba) liistolytica has been proved to be pathogenic, causing 

 dysentery and liver abscess. 



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