200 THE AMERICAN NATURALIST [Vol. LIV 



from a process of torsion of the synaptic mates about 

 each other, followed by a partial fusion between them at 

 certain points where threads from opposite sides of the 

 spiral have come together, crossing each other to form a 

 "chiasma" at each such point. By a subsequent read- 

 justment of position the regions between these points of 

 partial fusion have opened out to form rings disposed at 

 right angles to one another, and connected at the points 

 where the chiasmas have been formed. The general 

 nature of this rather complicated conception may better 

 be grasped by a study of Fig. 4C than from a description. 

 Janssens assumes, further, that at some period in their 

 history the rings are cut through at these points of fusion 

 in such a manner as to effect an exchange of correspond- 

 ing regions between the synaptic mates. The effect, as 

 conceived by Janssens, is shown in Fig. 1 (copied from 

 Janssens), and more in detail in mv interpretative Fig. 

 4 C, C. 



Janssens 's general interpretation (as will at once ap- 

 pear from his diagrams here reproduced as Figs. 1 and 

 2 A-E) includes two more specific assumptions on which 

 the whole matter turns. These assumptions are : (1) that 

 all the rings are essentially alike, the synaptic mates, or 

 corresponding regions of them (black and white in the 

 figure) lying in every case on opposite sides of the ring- 

 opening, the longitudinal cleft in each thus representing 

 the future equation-division; from this it follows (2), 

 that rings which lie in the equatorial plane of the spindle 

 (horizontally) are divided equationally, while the alter- 

 nate rings that lie tangential to the spindle are cut cross- 

 wise, and hence reductionally, by the same division. Both 

 these assumptions differ wholly from the results of pre- 

 vious investigators and hence call for critical exami- 



The genesis and later history of the compound (espe- 

 cially the double) rings has been most fully studied in 

 the Orthoptera, having first been considered by McClung 

 and Granata, and more recently investigated with greater 



