GAMETIC MEIOSIS IN MONOCYSTIS. 



GARY N. CALKINS AND RACHEL C. BOWLING. 



The monocystids of the earthworm, probably the commonest 

 and most frequently found type of gregarine, have never been 

 completely monographed, although an excellent start in this 

 direction was made by Hesse (1909). Cytological studies have 

 been made by Wolters (1891), Cuenot (1901), Shellack (1912), 

 and Mulsow (1911), the latter finding typical gametic meiosis or 

 chromosome reduction in a species which he regarded as new and 

 to which he gave the name Monocystis rostraia. In this form 

 which he named from the presence of an attenuated proboscis-like 

 end of the cell, he found eight chromosomes of characteristic form 

 and size. This number of chromosomes was found in the first 

 nuclear spindle of the gamont after metamorphosis of the vege- 

 tative nucleus, and the same number was present in the successive 

 spindles of the succeeding progametic nuclei and until the final 

 division when the gametes are formed. In this ultimate division 

 Mulsow found that whereas eight chromosomes are present in the 

 nuclear plate of the mitotic figure at the metaphase only four 

 chromosomes are present in the daughter plates of the anaphase 

 stage and only four chromosomes are present in each of the two 

 resulting gametes. Here then the haploid number of chromo- 

 somes is characteristic of only one set of cells, viz. the gametes, of 

 the entire life cycle. Upon fusion of two gametes the diploid 

 number is restored and this diploid number is characteristic of the 

 entire vegetative cycle including all of the progametic nuclei. 

 The actual reduction in number of chromosomes according to this 

 account agrees in point of time with the corresponding meiotic 

 phase in the great majority of the metazoa, a type which Wilson 

 describes as gametic meiosis. 



A very different time of reduction in chromosome number was 



described by Dobell in connection with gamete formation, 



fertilization, and metagamic divisions of the coccidian Aggregate, 



eberthi, and by Jameson in connection with the gregarine Diplo- 



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