:i 



PARASYNDESIS AND TELOSYNDESIS 



45 



iefinitive bivalents out of the pachytene loops as depicted by Farmer and 

 yioore. It will be noticed that the longitudinal slit, faintly visible here 

 md there in the pachytene stage (A, and A') appears from these figures 

 to be traceable into the slits occasionally indicated in each constituent 

 of the bivalents, and therefore represents the division plane of the second 

 division of the meiotic phase. 



It would take too much space to discuss fully the relative merits of 

 the two theories, but the most important pros and cons can be briefly 

 summarized, remembering that it is impossible to reconcile the divergent 



Fig. iS. 



Illustrating telosyndetic view of meiosis. (A-C, after Farmer and Moore, Q.J. M.S., 1905.) A-C, three 

 stages in the formation of the bivalents in Osmnnda rcgalis. A'-C, their interpretation according to the telo- 

 syndetic view. * Supposed points of junction of the longitudinally split constituents of each bivalent. 



views by the simple assumption that parasyndesis holds for some species 

 and telosyndesis for others. For the disputed stages — zygotene and 

 diplotene — are too similar in many of the species which have been inter- 

 preted in opposite senses to have been brought about by such different 

 processes, and, moreover, in many instances opposite accounts have been 

 given of the same spgcies. 



I. The overwhelming balance of evidence of actual observation 

 appears to the author and many others (including the older cytologists 

 who were not interested in either theory) to favour the view that the 

 diplotene and diakinetic figures are produced by the reopening of the 



