274 Transactions of the Society, 



Since the two views are mutually exclusive, and since the 

 phenomena are in many points essentially similar in all cases, it 

 is difficult to accept as a compromise the existence of both modes 

 of union. In attempting an evaluation of both sides of the contro- 

 versy it must be remembered that the diplotene threads often pass 

 through a complicated series of changes in the process of tranform- 

 ing into the heterotype chromosomes, so that satisfactory evidence 

 of the relation of the transverse cleavage of the latter to the 

 longitudinal split in the former can only be obtained if the history 

 of individual chromosomes is studied as Wenrich (1917) has done. 

 Secondly, it must be conceded that the parasynaptic accounts have 

 been based on some of the most favourable material for study 

 (Batrachoseps and Lepidosiren). Finally, in a large number of 

 cases where early investigators described a telosynaptic transforma- 

 tion of the lieterotype chromosome, and denied the existence of a 

 diploid leptotene stage, subsequent workers have disagreed with 

 their conclusions. This applies not only to the work of Gold- 

 schmidt, Arnold and others on Flatworms, which has been denied 

 by Gelei and later workers, but to all the earlier work on the 

 Orthoptera. In regard to the latter it is only necessary to mention 

 the namay of Morse, Mohr, Steevens, Vejdovsky, Gerard, Eobertson, 

 Wenrich, Otte, all of whom have adopted the theory of parallel 

 conjugation ; and the work of Metz and others showing the lateral 

 association in pairs of the chromosomes in the somatic complex of 

 Diptera has increasingly influenced cytologists in favour of para- 

 synapsis. 



In opposition to both schools Duesberg has attacked the whole 

 theory of synapsis from a study of the meiotic phase itself. 

 Duesberg's own work on the spermatogenesis of the Eat has been 

 very destructively criticized by Allen ; but as his general thesis has 

 certain points in common with views held by botanical cytologists 

 it merits (brief) comment. Briefly, he holds that the events of the 

 meiotic phase are not essentially different from those of a normal 

 prophase. Now a comparison with a normal prophase must be 

 based upon similarity in number, size and shape or disposition of 

 the chromatin elements. As regards number Duesberg is content 

 to neglect the witness of reliable workers who claim that the full 

 diploid number of leptotene threads is present at the inception of 

 the meiotic pliase. With respect to the form of the chromatic 

 elements there is obviously no basis of similarity between the 

 leptotene threads and the tlocculent prochromosome of a normal 

 prophase ; while the polar orientation of the meiotic nucleus is a 

 phenomenon which Duesberg is content to dismiss from serious 

 consideration on tlie basis of his own incomplete observations on the 

 rat. It is true to say that the majority of competent cytologists 

 are com[)elled to recognize in oi)position to this view that the 

 meiotic phase in the nucleus is an event sui generis. 



