The FroUem of t^yna]_)sis. 275 



Some cytologists have attempted to draw a too detailed com- 

 parison between the phenomena of the meiotic phase in animals 

 and plants, consequently the issue has been very much complicated, 

 for reasons that will appear. As early as 1905 Farmer and Moore 

 formulated a theory of meiotic phase in plants and animals based 

 upon a comparison of a series of types (Osmunda, Feriplaneta, 

 Lilium) and advocating a telosynaptic interpretation . The principal 

 animal type, Penplaneta, was selected, unfortunately, owing to the 

 peculiar difficulties of Orthopteran spermatogenesis; and subsequent 

 work has made it clear that the Blattids in reality conform to the 

 theory of parallel conjugation. Since then the terms " telo- 

 synapsis " and *' parasynapsis " have come into use in botanical 

 cytology in a sense altogether different from that in which they 

 are employed in zoology. Of the two contractions of the chromatin 

 threadwork in the preineiotic phase of plants the telosynaptic theory 

 identifies the second, the parasynaptic theory the first, as the point 

 at which synapsis of homologous chromosomes is effected. Gregoire 

 has compared the first contraction stage of plants to the bouquet 

 stage in animals (1906-11), thus aggravating the confusion in existing 

 terminology. Now, Miss Digby (1919) has shown recently that 

 in Osmunda the archesporial chromosomes undergo cleavage in the 

 telophase, and that the fusion witnessed in the first contraction 

 stage of the meiotic nucleus is in reality the reassociation of lialf- 

 chromosomes split in anticipation of a division which is arrested. 

 In view of the fact that wherever the leptotene threads in animals 

 can be definitely counted their number corresponds to the telophasic 

 chromosomes, and also the possibility of tracing them back to the 

 latter in a number of cases (e.g. "Wilson in Hemiptera), it may be 

 stated without hesitancy that the data embodied in the interpreta- 

 tion of the first contraction phase of plants by Farmer, Digby, Gates 

 and others have no bearing on any stage which occurs normally in 

 animals. 



Turning now to the bearing of the study of the meiotic phase 

 on the general theory of synapsis derived from a consideration of 

 the heteromorphism of chromosome complexes, the principal 

 questions that arise are, first, whether there is actual evidence that 

 chromatin elements conjugate ; second, whether such elements are 

 chromosomes sensu stricto ; lastly, whether the conjugating elements 

 are subsequently disjoined by a reduction- division. As regards 

 the first, all those who advocate parasynapsis in animals are agreed ; 

 concerning the second, a few authors (e.g. Wilson) claim to have 

 established continuity between the telephase chromosomes and the 

 conjugating filaments ; while with respect to the last, the fusion of 

 the conjugating elements in parasynapsis is usually so complete 

 that it is almost impossible to be certain that they do not lose 

 their individuality, as believed by Vejdovsky and Bonnevie. It 

 will thus be seen that w^hile the ' chromosome hypothesis has 



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