608 FERTILIZATION 



isms are too widely dispersed or too effectively isolated by barriers, there 

 will be no progeny. This difficulty simply does not exist for autogamous 

 organisms, as the isolated individual can reproduce itself sexually with- 

 out recourse to others of its kind. 



Several cases of self-fertilization have already been pointed out {Acti- 

 nosphaerium, Act'mophrys, Sappinia?) . In these cases fertilization is ac- 

 complished by the fusion of sister cells, which have undergone nuclear 

 reorganization (perhaps reduction). This type of autogamy has been 

 called pedogamy. 



Another type of autogamy is common in the Cnidosporidia and is 

 known best in the Myxosporidia. Here the nucleus divides to form several 

 nuclei, without division of the cytoplasm. The nuclei then reunite in 

 pairs, to form amphinuclei. 



In the myxosporidian Sphaeromyxa sabrazesi, according to Schroder 

 (1907, 1910), the plasmodial body contains two kinds of nuclei. Small 

 areas become differentiated from the surrounding protoplasm. Each area, 

 or pansporoblast, contains two nuclei, one large and one small. Both of 

 these nuclei divide to form seven, so that there are fourteen nuclei pro- 

 duced in each pansporoblast. The pansporoblast divides into two halves, 

 the sporoblasts, which are destined to become the two spores. The 

 daughter sporoblasts receive six nuclei apiece, and the other two nuclei 

 are expelled at the fission of the pansporoblast and degenerate as "re- 

 duction nuclei." Of the remaining six in each sporoblast, two form the 

 capsule and shell, two form the polar capsules, and two presumably one 

 of each original kind, remain as the pronuclei and later fuse with each 

 other in autogamous fertilization. More recently Kudo (1926) has 

 described a somewhat similar case of autogamy in Myxosonia catostomi. 



Debaisieux (1924) found six chromosomes in the early mitoses of 

 the Plasmodium of Sphaeromyxa sabrazesi. In later stages he found the 

 number reduced to the haploid three, 



Naville (1930b) is very specific in his account of this species (Fig. 

 145) and of S. balbianii. In both forms four chromosomes are reduced 

 to the haploid two in the plasmodium, just before the formation of the 

 pansporoblast and after the differentiation of the nuclei into large and 

 small types. The two types he calls macrogametocytes and microgameto- 

 cytes, because they are surrounded by a zone of condensed cytoplasm. The 

 union of two of these zones of cytoplasm in plastogamy brings a large 



