FERTILIZATION 595 



each individual give rise to the nuclei of amoebulae, which bud off and 

 grow into new adults. Zuelzer (1904) described chromidiogamy in D//- 

 flugia urceolata, but in this case all the chromidia are said to fuse into 

 a single mass, and the united protoplasmic bodies condense and form a 

 cyst. New nuclei form from the chromidia. 



The significance of chromidiogamy has never been satisfactorily ex- 

 plained; in fact, the existence of the process itself remains in consider- 

 able doubt. While it is true that specimens of Arcella may frequently 

 be found in which no typical nuclei are visible and the cytoplasm of 

 which may contain numerous chromidia, these may be degenerating 

 forms, and only a thoroughgoing reinvestigation of the life history of 

 this interesting organism will convince the skeptics or disillusion the 

 credulous. 



In Elpatiewsky's account of anisogamy, some individuals form macro- 

 gametes by repeated nuclear division, while others form microgametes. 

 The gametes are amoebulae, and the difference between male and fe- 

 male is one of size. After copulation between large and small gametes, 

 the zygotes grow up into adult arcellae. 



A remarkable type of sexual process was described by Hartmann and 

 Nagler (1908) in Sappinia [Amoeba) diploidea, a binucleate form 

 (Fig. 141). The active organism contains two nuclei, derived originally 

 from two parents. It is therefore a kind of adult prezygote. Two such 

 binucleate amoebae come together and develop a common cyst, but their 

 bodies do not fuse. In each amoeba the two nuclei now fuse in a long- 

 delayed fertilization, or karyogamy, after first giving off "vegetative 

 chromidia." The cytoplasms of the two amoebae now fuse completely. 

 Each synkaryon undergoes two "reduction divisions," after which three 

 products of each degenerate, leaving one reduced nucleus from each 

 synkaryon. These two are the nuclei of the vegetative form. If these two 

 divisions are in reality meiotic divisions, the organism lives a haploid 

 existence, and constitutes the only known case of zygotic reduction in 

 the Sarcodina. If not, some other interpretation must be found for the 

 two divisions which follow syngamy. Since chromosome number and 

 behavior are not known in this form, no satisfactory conclusions may 

 be drawn. It may be argued, of course, that the two haploid nuclei, lying 

 close together in the cytoplasm, are the equivalent of one diploid nucleus, 

 but such speculation must await the positive determination of the chromo- 

 some behavior. 



