The Chromosome Cycle in Coccidia and Gregarines. 93 



exception of the zygote nucleus. This is a diploid nucleus, containing two 

 haploid groups of chromosomes derived from the two gamete nuclei which 

 entered into its formation. The division of this nucleus is, in both Aggregata 

 and Diplocystis, a reduction division, which reduces the diploid number to the 

 haploid once more. From the point of view of the chromosomes, it is thus 

 clear that the first division of the sporont nucleus of Aggregata is not 

 homologous with the first division of the " sporont " (gamont) nucleus of 

 Diplocystis, but with the first division of its spore nucleus — since these are 

 the divisions during which the chromosome numbers are halved. 



A chromosome cycle such as we have found in the two members of the 

 Sporozoa here described has not, we believe, been previously demonstrated in 

 any of the Protista. It has, however, been supposed — though not proved — 

 to occur in some forms. 



We regard the supposition that reduction occurs during gametogenesis in 

 the Coccidia and Gregarines as an incorrect analogy drawn from other 

 animals. The Coccidia and Gregarines are a very homogeneous group of 

 organisms. And the chromosome cycle is, as a rule, so constant a character 

 in any natural group of animals or plants, that we find every reason to believe 

 at present that the chromosomes of the Sporozoa* generally will be found — 

 when more fully studied — to behave like those of Aggregata and Diplocystis. 

 There is at least, we believe, no evidence from other Coccidia, and but little 

 from other Gregarines, which can be iirged with any cogency against this 

 view. 



KEFEKENCES. 



Dobell, C. (1914). " Le cycle eVolutif de V Aggregata" ' Bull. Inst. Oceanogr. Monaco,' 

 No. 283. 



Kunstler, J. (1887). "Diplocystis schneideri (nov. gen., nov. sp.)," ' Tabl. Zool.,' vol. 2, 

 p. 25. 



Leger, L., and Duboscq, O. (1908). "L'evolution schizogonique de V Aggregata (Eucoc- 



cidium) eberthi, Labbe," 'Arch. f. Protistenk.,' vol. 12, p. 44. 



(1909). " Etudes sur la sexualite chez les Gregarines," Ibid., vol. 14, p. 19. 



Mulsow, K. (1911). "Ueber Fortpflanzungserscheinungen bei Monocystis rostrata, n. 



sp.," Ibid., vol. 22, p. 20. 

 Paeliler, F. (1904). " Ueber die Morphologie, Fortpflanzung und Entwicklung von 



Gregarina ovata," Ibid., vol. 4, p. 64. 

 Schaudinn, F. (1900). " Untersuchungen iiber die Generationswechsel bei Coccidien," 



'Zool. Jahrb. (Anat.),' vol. 13, p. 197. 

 (1902). " Studien iiber Krankheitserregenden Protozoen. — I. Cyclospora caryolytica 



Schaud., etc.," ' Arb. a. d. kaiserl. Ges.-Amt.,' vol. 18, p. 378. 



* By " Sporozoa " we mean the so-called Telosporidia only. We regard the 

 " Neosporidia : ' as totally unrelated organisms. 



