366 EDMUND B. WILSON 



In certain cysts that obviously precede those of Stage b the 

 nuclei are still smaller, the sex-chromosomes more elongated, while 

 the autosomes form a lightly staining, vague net-like structure 

 in which individual chromosomes can not be distinguished. This 

 stage evidently corresponds to Davis's 'Stage a' in the Orthop- 

 tera, and is well shown in McClung's preparations. A similar 

 stage has been described by several other students of the Orthop- 

 tera, especially by McClung. 



It is difficult to represent these nuclei accurately in drawings; 

 but a fairly good idea of them may be obtained from figs. 68 to 70, 

 which are from careful studies. They seem to contain a rather 

 coarse and close network, with thickened and irregular nodes of 

 varying size and number. In both species the sex-chromosomes 

 are more elongated than in Stage b, and in Lygaeus the X-chro- 

 mosome often assumes an almost vermiform shape, as is shown 

 in the figures. That these nuclei follow almost immediately 

 upon the last spermatogonial telophase is proved both by their 

 small size and by the transitional stages seen in the same nuclei. 

 This is most clearly seen in Lygaeus, where the elongate X-chro- 

 mosome enables us to identify the early spermatocytes with cer- 

 tainty (these chromosomes do not appear as condensed bodies 

 in the spermatogonial nuclei). In the cyst from which figs. 68 to 

 70 were drawn both sex-chromosomes are perfectly clear in many 

 of the nuclei, but in many the F-chromosome can not be found, 

 and in a considerable number of nuclei, which seem to lie entirely 

 within the section, not a trace of either sex-chromosome can be seen 

 (fig. 68). In this particular cyst no spermatogonial divisions are 

 seen ; but in other cysts in the same region of the testis, nuclei of 

 exactly the same type as those last mentioned (with neither sex- 

 chromosome in evidence) are seen together with the spermatogonial 

 anaphases. That the latter are the final spermatogonial divisions 

 can not be proved; but in Lygaeus the evidence seems nearly 

 decisive that there is a short period following the last division in 

 which the identity of all the chromosomes is lost to view. I believe 

 this to be true also in Oncopeltus, though the evidence is less satis- 

 factory. On the other hand, it is possible that in Largus the final 

 anaphase-chromosomes give rise directly to the massive bodies of 



