422 ELMER L. SHAFFER. 



spindle axis with the sister chromatids directed toward the same 

 pole. Polar views of the metaphase (Fig. 55) show only half 

 the tetrad, but oblique views show the relation clearly (Fig. 57). 

 Thus the rings of Cicada are of the Stenobothrus type and they 

 divide reductionally in the first maturation division. 



(c) Synapsis. Although I have been unable to study the 

 process of synapsis in the male germ cells, my observations on 

 the oocytes indicates that the chromosomes conjugate para- 

 synaptically, and there is no reason for supposing that it might 

 be different in the spermatocytes. From Fig. 38 it is quite 

 evident that the leptotene threads pair side-to-side, but the 

 essential point is whether each leptotene thread actually repre- 

 sents a single univalent oogonial chromosome. Wenrich ('16) 

 has shown in Phrynotettix that the leptotene threads are derived 

 from the telophase chromosomes of the last spermatogonial 

 division by a process of unravelling of the chromatic blocks 

 contained within separate chromosomal vesicles. In Cicada I 

 have been unable to trace the oogonial telophase chromosomes 

 into the early growth stages of the oocyte, but there is some 

 indirect evidence that each leptotene thread is derived from a 

 single oogonial chromosome. In the late leptotene stages, the 

 threads are well polarized and all extend in one direction through 

 the nucleus. I have studied a great many such nuclei in cross- 

 section and it is possible to count the number of leptotene threads 

 cut on end view. Such counts usually approximate the diploid 

 chromosome number (20) and points to the fact that each lepto- 

 tene thread is derived from a single chromosome. 



As has been noted before (page 417), a casual study of the 

 germinal vesicles of the oocytes does not indicate any persisting 

 individuality of the chromosomes; however, careful and minute 

 analysis of such nuclei reveals the fact that the synaptic threads 

 are still present but in a much-expanded and diffuse condition. 

 Similarly in the male germ cells following the strepsistene stages, 

 the synaptic threads appear to loose their individuality, becoming 

 diffuse and widely expanded ("confused stage" of Wilson). This 

 diffuse stage in the spermatocytes, although of relatively short 

 duration, is no doubt homologous to the "germinal vesicle" 

 stage of the oocyte, since both occur at homologous periods in 



