CHAPTER VIII 

 SYNGAMY AND SEX IN THE PROTOZOA 



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IT is a matter of common knowledge that amongst all the higher 

 animals and plants the phenomena of sexual generation and sexual 

 differentiation are of universal occurrence. Reduced to its simplest 

 terms, and stripped of all secondary complications, the sexual 

 process in an ordinary animal or plant consists essentially of the 

 following series of events : In the multicellular body certain cells 

 are produced which may be termed comprehensively and universally 

 the gametes. In the two sexes the gametes exhibit characteristic 

 differences ; those of the male sex, the spermatozoa, are typically 

 minute, active, and produced in large numbers ; those of the female 

 sex, the ova, are, on the contrary, relatively bulky, inert, and 

 produced in far fewer numbers. The gametes are set free from the 

 body, or, at least, from the organs in which they arise, and each 

 male gamete, if it finds a partner and if circumstances permit, 

 unites with a female gamete ; their bodies fuse completely, cell 

 with cell and nucleus with nucleus, and the product is a " fertilized 

 ovum," or zygote, a single cell which proceeds to multiply actively 

 by cell-division, the final result being a new multicellular individual. 



In the Protista belonging to what has been termed in the first 

 chapter of this book the " cellular grade" that is to say, in the 

 Protozoa and the unicellular plants sexual phenomena are also of 

 widespread, probably of universal, occurrence, and the process of 

 sexual union differs only in unessential points from that seen in 

 higher organisms. 



In the first place, since the individual in Protozoa is a single cell, 

 the gametes themselves are also complete individuals, modifica- 

 tions merely of the ordinary individuals of the species produced at 

 certain periods or phases of the life-cycle. 



Secondly, the differentiation of male and female gametes rarely 

 attains to the high degree seen in the Metazoa, and may be nil ; 

 the two gametes may be perfectly similar in all perceptible features 

 of structure or constitution, as, for example, Copromonas (Fig. 111). 



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