REPROD UCTION 57 



In Monocystis rostrata, a parasite of the earthworm, Muslow 

 noted that the nuclei of the two gregarines which encyst to- 

 gether, multiply by a mitosis in which eight chromosomes are 

 constantly present, but in the last division of gametic differen- 

 tiation each daughter cell receives four chromosomes. In 

 another species of Monocystis of the same host, Calkins and 

 Bowling found that the normal number of chromosomes is ten, 

 and that it is halved in the last gametic division. It will be seen 

 from these that the zygote will contain the normal number of 

 chromosomes. 



On the other hand, in the coccidian, Aggregata eberthi 

 (Dobell, 1925; Belaf, 1926), and in the gregarine, Diplocystis 

 schneideri (Jameson, 1920), there is no reduction in the number 

 of chromosomes during the gamete-formation and, therefore, 

 the resulting zygote contains twice the typical number of chro- 

 mosomes. The first zygotic nuclear division was found to be 

 meiotic, thus restoring the number of chromosomes in each 

 nucleus. 



Paedogamy 



In a few forms, it has been observed that the organism di- 

 vides into two uninucleate individuals, and that the two bodies 

 fuse completely into one after a reduction division of the nuclei. 

 This process has been named paedogamy. Perhaps the classical 

 example is that which was found by Hertwig (1898) in Actino- 

 sphaerium eichhorni. The organism encysts within a capsule, 

 and the body divides into numerous uninucleate secondary 

 cysts. The protoplasm of each of the latter divides into two cells 

 and remains within a common cyst-wall. Their nuclei divide 

 twice, and all the division products in each cell degenerate 

 except one. Nuclear and cytoplasmic union between the two 

 occurs, and a zygote is thus formed. 



Autogamy 



In some instances, the nucleus or nuclei divide once or twice 

 without any division of the cytoplasm. The nuclei then fuse in 

 pairs with one another after throwing off a certain portion of 

 the chromatin material. This has been called autogamy. Un- 

 doubtedly several cases of so-called autogamy were due to mis- 

 interpretation, but in some Microsporidia, such a process has 



