PHENOMENA ACCOMPANYING FERTILIZATION 



533 



first division of the zygotes the two sets of chromosomes unite 

 in homologous pairs; in Aqcjregata 1 pair consists of long chromo- 

 somes, 1 pair is very short and 4 pairs are intermediate in length 

 (Fig. 222). The nuclei resulting from this first metagamic division 

 have 6 chromosomes each in Aggregate! and 3 each in Dip- 

 locystis and these haploid numbers are retained throughout the 

 vegetative cycles. 



The generalization made by Dobell and Jameson to the effect 

 that this method of reduction is probably universal among the 

 Telosporidia is hardl\' justified by these two cases. Few species 

 indeed have been studied with respect to the reduction of chromo- 



B 



C 



D 



Fig. 223. — Diplocystis schneideri. Zygotic meiosis. A to E. nucleus of the zygote 

 forming 6 chromosomes (the diploid number), and the first metagamic division; F, 

 anaphase of the sixth progamous division preparatory to gamete formation, with 

 3 longitudinally split chromosomes, the haploid number. (After .Jameson.) 



some number and only one— Monocystis rostrata—hy ]\Iulsow 

 (1911), with sufficient care as to cytological detail to be admitted, 

 and here as stated above, reduction occurs with the final progamous 

 division of the nuclei. Dobell and Jameson would explain this 

 divergent case as due to confusion by Mulsow of stages of two dif- 

 ferent gregarines one with 8 the other with 4 chromosomes, but 

 before sweeping away a difficulty in this naive manner it would be 

 well to reexamine Monocystis rostrata in the light of the more recent 

 work. Evidence in support of Dobell and Jameson's generalization 

 is furnished by the fact of the frequent occurrence of an odd number 

 of chromosomes in nuclei of different gregarines. Thus 5 chromo- 

 somes were found by Shellack (1907) in Echinomera hispida and 



