MALE GERM CELLS IN NOTONECTA 93 



the plane of the ring and is therefore probably an equation 

 division. 



In many cases the ring goes on to the metaphase spindle with- 

 out further modification, e.g., in the vertebrates and higher 

 plants, annelids, etc., but in some cases, e.g., the insects and 

 copepods, it condenses into a tetrad, as first explained in detail 

 by Paulmier ('98). In other forms where the ring condenses, the 

 split is either entirely lost before the second division or is only 

 faintly indicated b}'- an indentation. In most forms in which no 

 condensation takes place, the identity of the chromosomes is lost 

 in the interkinesis, although in Tomopteris, the Schreiners ('06a) 

 have traced the second longitudinal split with some degree of cer- 

 tainty to the second division. In Notonecta, the ring condenses 

 to form a tetrad, but the longitudinal split remains most distinct. 

 In N. insulata in the case of two chromosomes and in N. irrorata 

 in the case of one chromosome, in the first metaphase, the chromo- 

 some is completely divided into two parts and it remains thus 

 until drawn on the second spindle. The second division follows 

 directly on the first, the telophase of the first being the prophase 

 of the second. Since this split can be traced from the early 

 prophase of the first division to the second metaphase when it 

 lies in the equatorial plane, there can be absolutely no question 

 as to its identity with the division line of the second division. 



The cross is in principle the same as the ring, as first pointed 

 out by Paulmier ('98) and as more recently discussed from the 

 point of view of parasynapsis by the Schreiners ('06 a,b) and 

 Montgomery ('11), the difference in form being due to the diver- 

 gence of the two parallel rods from the ends (cross) instead of 

 in the middle (ring). In the process of condensation the cross 

 becomes a typical tetrad in contrast to the ring-tetrad, whose 

 quadripartite nature is not detectable in lateral view since the 

 second longitudinal split lies in the plane of the spindle. The 

 similarity between the two is easily seen however, if we compare 

 a lateral view of the cross-tetrad with an end view of the ring- 

 tetrad (cf. fig. 104 H with 95 B). The first division plane passes 

 across the short axis of the cross-tetrad, and if we consider each 

 original parallel rod as a univalent chromosome this is a reduc- 



