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The Chromosome Cycle in Coccidia and Gregarines. 

 By Clifford Dobell and A. Pringle Jameson. 



(Communicated by J. Bretland Farmer, F.B.S. Beceived May 13, 1915.) 



Despite the large amount of work which has already been devoted to the 

 study of the Coccidia and Gregarines, very little indeed is known definitely 

 about the behaviour of the chromosomes in these Protozoa. Not only has the 

 chromosome cycle been left uninvestigated and undescribed in the majority of 

 these organisms which have hitherto been studied, but the very existence of 

 chromosomes in the nuclear divisions at many stages in the life-history of 

 certain forms has even been denied ; and the most contradictory and unsatis- 

 factory accounts have been given of that most important phase in the life- 

 cycle of the chromosomes — the phase of meiosis, or reduction. 



In order to fill up this gap in our knowledge of the Sporozoa, we have made 

 — during the last few years — a very detailed study of the chromosomes of a 

 coccidian and a gregarine. One of us (C. D.) has investigated the coccidian* 

 Aggregate/, eberthi Labbe, whilst the other (A. P. J.) has studied the gregarine 

 Diplocystis schneideri Kunstler. Careful investigation of these two organisms 

 has shown that the nuclear divisions at all stages in the life-histories are 

 mitotic, and that the chromosome numbers are remarkably constant. 



As our results are, we believe, quite definite and conclusive, and as the 

 publication of them in full is likely to be unavoidably delayed for some time, 

 we think it desirable to place them on record. Complete accounts of the life- 

 histories of Aggregata and Diplocystis we hope to publish separately elsewhere. 

 We shall here deal only with the essential facts which we have established 

 concerning the chromosomes of these two forms. 



1. The Chromosomes of Aggregata eberthi. 



The life-history of this coccidian comprises a sexual generation which takes 

 place in the body of a cuttle-fish (Sejria officinalis), and an asexual generation 

 in the body of a crab (Portunus clcpurator). These generations are of the 

 usual coccidian type. In the sexual cycle, male and female individuals 

 (" microgametocytes " and " macrogametocytes ") are formed, which give rise 

 to raicrogametes and macrogametes respectively. Each of the latter is 

 fertilized by one of the former ; and after the union of the two nuclei, the 

 zygote nucleus divides many times to form the nuclei of the numerous 



* That this organism is really a coccidian and not a gregarine has already been shown 

 (c/. Dobell, 1914). 



