No. 632] CHIASMATYPE AND CROSSING OYER 209 



which at least suggest a process of torsion or strepsi- 

 nema-formation in the early diplotene prior to, or very 

 early during, the definitive opening out of the prophase- 

 figures— e. g., in Wenrich ( '16), Fig. 75, or ( '17), Fig. 23, 

 and in Eobertson ('16), Figs. 149, a and b. The case 

 seems, therefore, by no means closed; and we may await 

 the publication of Janssens's new results in greater de- 

 tail, in the hope that more definite evidence may now be 

 produced concerning the critical point at issue. 



My own doubts on this matter first grew out of obser- 

 vations on the origin of the double crosses, which, a- 

 above indicated, involve a similar question concerning 

 the chiasmatype. Janssens's earlier interpretation of 

 the double cross, which I believe he was the first to offer, 

 was in principle the same as that briefly indicated 

 above and schematically shown in Figs. 5, III and 

 6 D-E. Later this interpretation became the prevalent 

 one but was abandoned by Janssens himself ( '09, '19) in 

 favor of one which assumes a process of chiasmatype to 

 be involved in the cross-formation. This interpretation 

 starts with a comparison of the double cross to the region 

 at which two rings join; and this is obviously correct 

 under any theory (cf. Figs. 3 D and 6 C, F). Janssens, 

 however, assumes the relation between the synaptic 

 mates to be essentially as shown in the diagram here 

 reproduced as Fig. 6 A-B, the two synaptic mates being 

 bent at right angles, and united by their apices to form a 

 cross which then splits straight through all four arms, 

 thus giving two cross-over chromatids out of four. I 

 seriously considered this interpretation in my own studies 

 on the double crosses of Hemiptera, but finally became 

 convinced ( '12 and subsequently) that it does not corre- 

 spond with the facts. More recently Eobertson, Wen- 

 rich and Mohr have demonstrated the same conclusion 

 in a very circumstantial and convincing manner in case 

 of the double crosses of Orthoptera, tracing their origin 

 step by step from the original diplotene in the manner 

 indicated in Fig. 5, HL According to all these observa- 



