1914] Snook-Long: Paras i/napsis in Ancicles lugubris 523 



With these facts and considerations in mind, it is concluded 

 that the V- and Y-figures do not indicate a splittint;'. as main- 

 tained by some, but that they represent a progressive, parallel 

 union or conjugation of fine (leptotene) threads; in other words, 

 a parasynaptic union. This union takes place during the amphi- 

 tene stage and leads to the formation of the single, thick, polarized 

 loops. There is no reason for confusing the split which does occur 

 in the stage following the formation of the loops (and which may 

 be the reverse of parasynapsis) with the union in the amphitene 

 stage, since the two stages are easily distinguishable both by their 

 appearance and position in the testis. 



The evidence set forth above does not warrant an assertion 

 that the conjugating leptotene threads are identical with the 

 spermatogonial chromosomes. Nevertheless, the fact that the 

 number of chromosomes (tetrads) in the first maturation spindle 

 is half that of the chromosomes in the spermatogonial division, 

 together with the evidence that the tetrads are formed by the 

 union of threads evolved from the nuclear network which in 

 turn is formed from the chromosomes of the last spermatogonial 

 telophase, suggests very strongly that the spermatogonial chro- 

 mosomes which went into the nuclear network reappear as the 

 pairing leptotene threads. This idea is further supported by the 

 manner in which the two branches of two Ys become continuous 

 as though they were the ends of threads (chromosomes) poten- 

 tially exifsting in the network, though not distinguishable as such. 

 Or, to reverse the conception, if it is considered that the sperma- 

 togonial chromosomes retain their continuity throughout the 

 resting .stage of the nucleus, then it is easier to comprehend why 

 the proper Y-figures become associated as the leptotene threads 

 are evolved, for the chromosomes, though in modified form and 

 only partly distinguishable as threads, begin to pair as they 

 might if pairing were delated until they were completely formed. 

 Although this way of stating the conception is open to the criti- 

 cism that it is an argument in a circle, still the conception is 

 worthy of consideration as having some weight on the positive 

 side of the question of the individuality of the chromosomes. 



It has already been pointed out that the stage of the polarized 

 loops which follows that of the conjugation of the leptotene 



