CHAPTER III 



REPRODUCTION IN PROTOZOA 



THE MODE of reproduction in the Protozoa is highly vari- 

 able among different groups, and even in the same group 

 it varies with differences in habitat. It will here be briefly 

 considered under asexual and sexual reproduction. 



Asexual Reproduction 



Nuclear Division 



Between a simple direct division on the one hand and a 

 complicated indirect division which is comparable to the mitosis 

 of a typical metazoan cell on the other hand, all kinds of nuclear 

 division are to be encountered. 



Direct nuclear division. While not so widely found as was 

 thought in former years, amitosis occurs without doubt in the 

 macronuclear division of the Ciliophora and in the nuclear divi- 

 sion of several Cnidosporidia and others. The macronucleus 

 elongates itself without any noticeable changes in internal 

 structure and becomes constricted through the middle, resulting 

 in the formation of two daughter nuclei, A typical example is 

 the division of the macronucleus as observed in Paramecium 

 caudatum (Fig. 16). When the macronucleus is an elongated 

 beaded form, as in Spirostomum amhiguum, the whole becomes 

 condensed into a rounded mass prior to the division. In Urolep- 

 tus mobilis, which contains normally eight or more nuclei, the 

 macronuclei, according to Calkins, after throwing off fine 

 granules and losing the nuclear cleft, fuse into one, preparatory 

 to a direct division (Fig. 17). The nucleus then divides twice or 

 three times before the cytoplasmic division occurs; the fourth 

 nuclear division appears after the daughter cells have become 

 separated completely. In Dileptus anser (Fig. 4), with scattered 

 nuclei or chromidia. Calkins has shown that the individual gran- 

 ules become elongated and divide where they happen to lie. 

 In Endamoeba hlattae, the nucleus of the trophozoite divides 



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