42 PROTOZOA 



sperm with the egg but no cytological proof of zygote formation has 

 been achieved. (2) Sporulation or encystment occurs in Ameba. 

 The animal becomes spherical, secretes three-layered cysts and 

 produces, by successive divisions of the nucleus, a multicellular 

 somatella containing 2, 4, 8 or more nuclei. The Ameba divides 

 at encystment into as many individuals as there are nuclei in the 

 somatella. These emerge through a pore from the cyst as amebulae 

 and in a few hours develop into full grown amebae. (3) Fission. 

 In some forms, division (binary fission) takes place during activity; 

 in others it takes place in a cyst. (4) Budding. In Euglypha, the 

 animal buds and new particles go out from the shell. Simple division 

 in Protozoa may lead to colony formation. (5) Conjugation in the 

 Sarcodina is general, except in Lobosa and an investigator thought 

 that he had seen it in Ameba proteus. This may have been only 

 agglutination. (6) There is no evidence of reorganization, or 

 endomixis (see page 44) in the Sarcodina. 



Regeneration in the Sarcodina. — The excision of one-fourth of 

 the cytoplasm of the Ameba has no effect on its division. Regenera- 

 tion may take place in twenty-four hours and division follows nor- 

 mally. Enucleated amebae can move, but are not able to carry on 

 other body processes and soon die. 



Reproduction in the Flagellata. (i) Fission. — With but few 

 exceptions the flagellates have longitudinal fission. (2) Encystment 

 and sporulation also occur at times. 



Reproduction in the Ciliata.^ (i) Fission. — All ciliates have 

 transverse division. The reproduction of the macronucleus is 

 usually by direct division with little evidence of spindle formation 

 or definite chromosomes. In less complicated types of division, 

 the division of the macronucleus is relatively simple. In some forms 

 the macronucleus elongates, then constricts to form two equal 

 portions, one passing to each of the daughter cells {Paramecium, 

 Colpoda). When two macronuclei are present, each divides inde- 

 pendently of the other {Oxytricha, Stylonychia). In some types 

 multiple macronuclei may contain nuclear clefts with large granules 

 which reproduce by division. Micronuclei, if multiple in the cell, 

 do not fuse. The chromatin contents may be in part distributed and 

 then unite into a long banded nucleus. No elimination of micro- 

 nuclear material occurs. Each one divides by mitosis, with a 



* Consult Robertson, M. 1929. Life cycles in the Protozoa. Biol. Rev., vol. 4, 

 no. 2, April. 



