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THE AMEBIC AN NATURALIST [Vol. LIV 



alternate rings— a process which would produce a condi- 

 tion identical so far as appearances go, in both structure 

 and mode of origin, with the compound ring as described 

 by Granata, McClung, Eobertson or Wenrich, but one 

 which has a quite different morphological significance. 

 Such an assumption seems to me to be logically implied 

 by Janssens's own account, though I am not sure that 

 such is actually his meaning. 



I have tried to illustrate this by the series of diagrams 

 shown in Fig. 4. A represents the compound ring in ac- 

 cordance with the results of McClung and his followers, 

 the synaptic mates being in black and white, respectively. 

 If, however, we assume this condition to have been pre- 

 ceded by a two-strand cross-over or chiasmatypy at each 

 node, the composition of the tetrad becomes that shown 

 in B or C. Either of these figures realizes the two spei- 

 cific assumptions of Jans sens earlier emphasized, 

 namely: (1) that the longitudinal cleft in every ring rep- 

 resents an equation-division (i. e., separates correspond- 

 ing halves of one synaptic mate in this particular part of 

 the tetrad), and (2) that a straight split through the 

 ring-series (such as is shown in Fig. 1 B) will now divide 

 half the rings equationally and the alternate rings reduc- 

 tionally. Both show recombinations in the same regions 

 {Aa, Cc, Ee) and in the same relative numbers in the 

 cross-over threads; but they are differently grouped, 

 owing to the fact that in one case (B) a cross-over has 

 taken place between the same pair of threads at every 

 node, while in C this occurs only at every other node, the 

 cross-overs taking place in regular alternation between 

 two different pairs of threads. As a comparison of Figs. 

 2 and 4 C will show, it is this latter form that corresponds 

 with Janssens 's interpretation. 



Janssens does not make it clear in his preliminary 

 papers whether he assumes the chiasmas to be cut 

 through during the actual division of the tetrad, though 

 I think is what one would naturally infer from his gen- 

 eral account and from his figures, especially of the double 



