CHAPTER XII 



FERTILIZATION IN PROTOZOA 

 John P. Turner 



Much has been written on the phenomena which accompany fertih- 

 zation in the Protozoa. For detailed analyses of this literature the reader 

 is referred to texts by Minchin (1912), Doflein-Reichenow (5th Ed. 

 1929), and Calkins (1933). The aim of this chapter is to give a bird's- 

 eye view of the subject, to present some of the more significant facts al- 

 ready discovered, and last and most important to point out the need for 

 investigation to determine those facts and principles still awaiting dis- 

 covery. 



If we consider sex to be essentially the formation of gametes and 

 the fusion of those gametes in the fertilization process, we are using the 

 term sex in a somewhat broader sense than if we limit it to the differ- 

 ence or distinction between the two sexes. In the Metazoa these phe- 

 nomena seem to be fairly uniform for all groups; consequently, when 

 the basic principles of the process are understood for one animal, those 

 same principles may be applied to all the higher animals. Until very 

 recently, however, the Protozoa were thought to belong in a different 

 category, and one did not apply to them the general laws which were 

 considered applicable to all other animals. 



With recent discoveries, more and more of these preconceived dif- 

 ferences have disappeared and we are now faced with the question of 

 how close we can draw the analogies in sex phenomena between the 

 Protozoa and the Metazoa. In other words, are the fundamentals of 

 sex, i.e., maturation of gametes and fertilization, common to all animals, 

 both metazoan and protozoan.^ If so, how similar or how dissimilar are 

 the processes, and if not, just how do they differ? No final answer can 

 be given to these questions in our present state of knowledge, but con- 

 siderable evidence may be pointed out that is extremely significant. 



In the Metazoa fertilization is accomplished by a small, active micro- 

 gamete (spermatozoon) penetrating and fusing with a large, nonmotile 



