614 FERTILIZATION 



Weschenfelder's observations have confirmed the suspicions of many 

 protozoologists that there exist other gregarines besides Diplocystis 

 schneideri which undergo zygotic meiosis. The problem of inheritance 

 in these forms presents some interesting possibihties to the geneticist. 

 All genes possessed by the two parent organisms are passed to the zygote; 

 therefore, if oocyst (sporoblast) characters can be differentiated and 

 mated, the immediate and direct effect of those genes may be observed 

 in the resulting zygote. Furthermore, a haploid organism whose charac- 

 teristics are controlled by a single set of chromosomes presents a rare 

 opportunity for unusual genetic and cytological studies. 



Significance of Fertilization 



The causes and effects of fertilization in Protozoa are subjects upon 

 which a great deal has been written and some significant data obtained. ' 

 The three conditions cited by Maupas (1889) as necessary for conjuga- 

 tion in ciliates are sexual maturity, diverse ancestry, and hunger. All 

 three of these contributing factors have been supported by evidence 

 from some later investigations and all three have been discounted by 

 other investigations. In many cases the investigators have been dealing 

 with different species of Protozoa. This in itself is probably responsible 

 for many of the conflicting conclusions that have been reached. As the 

 evidence accumulates, it becomes increasingly clear that different Proto- 

 zoa require different conditions for conjugation and copulation, and 

 that we are not justified in applying to all Protozoa conclusions derived 

 from one or two or even several species. 



Among the flagellates and rhizopods there are many organisms in 

 which sexual phenomena have never been reported and in which prob- 

 ably none exists. These forms, then, are able to reproduce indefinitely 

 by asexual means. Inherently, therefore, protoplasm does not seem to 

 require sexual union. 



At the other end of the sexual scale are found those Sporozoa and 

 Foraminifera in which the life cycle is an obvious fact, and in which a 

 sexual stage develops as one sector of that cycle, without which they 

 could not continue their existence. If generalizations were made from 

 these two kinds of organisms, there would be contradictions too obvious 

 to relate. 



For similar but less obvious reasons, we may partially account for 



