ORTHOPTERAN SPERMATOGENESIS 673 



elements tend to become ring-shaped, but sometimes fail to pass 

 the V-condition and then may be identified with the same sized 

 element in other cells. Such relations appear in the cells of Tropi- 

 dolophus, just referred to, and also in cells from Mestobregma 

 shown in figures 92 and 93. 



In many cases the approximation of the outer ends of the 

 chromosomes does not pass beyond their mere endwise fusion, 

 but in some species there is a marked tendency for this portion 

 of the chromosome to take on the same form as the inner end, 

 or to exceed this and to form a second ring. In such cases the 

 outer ring has its plane at right angles to that of the inner. Ele- 

 ments of this type appear in figures 21 to 26, 28 and 30. They are 

 lacking in the cells represented in figures 27 and 29 from the same 

 animal. A lateral view of an incomplete second ring is shown in 

 the chromosomes at figure 25 b and at the right of the row in 

 figure 97. 



All the possibilities of form, due to movements of the chroma- 

 tids within the plane of separation corresponding to the longi- 

 tudinal cleft of the homologous chromosomes, have been con- 

 sidered, and mention has been made of the movement of these 

 elements when they pass from the plane of the equatorial plate 

 to that of the spindle axis. The latter condition is added to the 

 other changes in form in varying degrees depending upon the extent 

 to which it has already taken place in the prophase. During 

 one or the other of these periods this gliding of daughter chroma- 

 tids along the plane of their cleft and the subsequent approxima- 

 tion of homologous chromatids in a plane at right angles to this 

 must occur. In Mecostethus all this transposition falls in the 

 metaphase, for the elements start this period as rods or V's ex- 

 tended in the equatorial plate. Polar views of such stages are 

 shown in figures 32 to 34, 37, 41 to 43, and 46, and in figures 35, 

 36, 39, 40 and 45 are lateral views. Figure 38 shows individual 

 chromosomes from different angles with a prophase chromosome 

 at the bottom for comparison. In this case it is demonstrated 

 beyond any question that the separation of the elements is along 

 the length of the chromosomes and that they recombine, for a 

 time, by the approximation of homologous chromatids in the 



