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Messrs. C. Dobell and A. P. Jameson. 



to imagine how the halving of the number could occur. It appears to us 

 highly probable that, as in D. schneideri, no reduction occurs at these stages 

 in any of these organisms. 



There are only two cases of alleged reduction during gameto genesis in 

 Gregarines in which chromosome counts have been made. Recently 

 Tregouboff (1914) claims to have established a reduction of this sort in 

 Stenophora juli. The chromosomes are said to be reduced from four to two 

 by an unequal nuclear division, which takes place in the macrogametes either 

 before conjugation, or during conjugation, or after conjugation. Tt is 

 impossible to examine Tregouboff's statements in detail here ; but a careful 

 investigation of his figures and descriptions leads us to believe that the 

 phenomena observed have been misinterpreted. The evidence presented at 

 least is far from establishing his contentions. 



The only other case in which reduction is said to occur during gameto- 

 genesis, and in which the chromosomes have been counted, is that of Mono- 

 cystis rostrata, described by Mulsow (1911). Here the chromosomes are 

 stated to be reduced from eight to four at the nuclear division immediately 

 preceding gamete formation. This account does not agree with those of 

 others in which " polar nuclei " have been described, and is very different 

 from what we have found in Diplocystis. From a careful examination of 

 Mulsow's work we are at present inclined to believe that he was in reality 

 dealing with two different species of Monocystis — one with eight chromosomes, 

 the other with four ; and that no reduction occurs during gametogenesis. 

 Unfortunately, the division which we regard, on analogy with D. schneideri, 

 as probably the reduction division — namely, the first nuclear division in the 

 spore — is not properly described by Mulsow. The investigation of this 

 division is, however, of the utmost importance for the establishment of his 

 claims. If Mulsow's interpretations are correct, we shall be forced to 

 conclude that the chromosome cycle of M. rostrata is fundamentally different 

 from that of D. schneideri, and from that which we believe to occur in other 

 Gregarines and in Coccidia. 



We consider that neither of the above cases — Stenophora or Monocystis — 

 is perfectly satisfactory, considered entirely on its own merits. And this is 

 not to be wondered at if the chromosome cycle of the Gregarines in general 

 is, as we believe, like that which we have found in D. schneideri. The 

 chromosomes are here present in their haploid number during gametogenesis, 

 and accordingly their reduction is not to be expected at this stage. 



It is clear that the chromosome cycle of Aggregata agrees, in principle, 

 with that of Diplocystis. In both forms the haploid number of chromosomes 

 is found in every nucleus throughout the entire life-history, with the single 



