STUDIES ON CHROMOSOMES 399 



conspicuous way from the earlier generations of cells in the testis; 

 and these are not to be ignored in the study of this problem. 



Another very striking fact in the case of Batracoseps is that the 

 two branches of the Y often give exactly the appearance of twist- 

 ing together to form the stem — a condition very clearly shown in 

 many of Janssens's figures, though I do not find it mentioned in 

 the text. The pictures seen in Tomopteris also sometimes sug- 

 gest a similar condition, though less clearly; but in neither case am 

 I entirely sure of the case, since the torsion often can not be seen. 

 A twisting together of the longitudinal halves of the diplotene- 

 threads at a later stage ('strepsinema') is of course a very familiar 

 fact; but I can find only a few indications here and there in the 

 literature of such a twisting at the synaptic stage. Two very 

 definite accounts of such a process have recently been given by 

 Agar ('11) in the case of Lepidosiren, and by Bolles Lee ('11) in 

 Helix. The latter author believes the double spiral to persist 

 as such in the succeeding pachytene stage. ''Jamais, a aucune 

 moment, meme dans les enroulements les plus etroits du bouquet 

 tasse, on ne voit rien qui puisse faire conclure a une fusion des 

 deux elements" (p. 70). It is quite possible that a close torsion 

 of the threads may explain the fact that it is in many cases diffi- 

 cult or impossible to distinguish a longitudinal duality for a cer- 

 tain time after the synaptic process is completed. 



Concerning synapsis in the Orthoptera I can only speak with 

 considerable reserve. Most observers of this group have con- 

 cluded that the longitudinal duality of the diplotene-threads is 

 due to a process of longitudinal splitting (McClung and all of 

 his pupils, Sinety, Montgomery, Davis, Buchner, Jordan, Granata, 

 Brunelli) and only a few have attributed it to parasynapsis (Otte, 

 Gerard, Morse) . The few observations I have been able to make 

 on McClung's preparations of Achurum, Phrynotettix and Mer- 

 miria nevertheless lead me to the impression that a side by side 

 union of leptotene-threads takes place here also. The case is 

 however much less clear than in the other forms since the polari- 

 zation is less marked, and the amphitene stage, though clearly 

 apparent in some cases, is correspondingly less conspicuous. 



