374 EDMUND B. WILSON 



which may be traced into and through the growth-periods.^ 

 It is however very doubtful whether the massive bodies of Stage 

 b can actually be traced individually back to the anaphase-chro- 

 mosomes of the preceding division, though this may be possible in 

 some forms. 



Stage d. The leptotene-nuclei. It is impossible to draw any 

 definite line of demarkation between this stage and the preceding 

 one, since they are connected by insensible gradations. An excel- 

 lent idea of these stages is given by Miss Hedge's careful drawings 

 (figs. 56 to 59; cf. photos. 7, 8). In the earlier nuclei the threads 

 still have a more or less spiral or wavy course, and still show dis- 

 tinct evidence of clumping together in masses. A little later both 

 these appearances are lost, and the threads form an evenly dif- 

 fused, delicate spireme, always separated from the nuclear wall 

 by a considerable clear space. Still later the threads become 

 somewhat thicker, more open in arrangement, and stain a little 

 more deeply (figs. 58, 59, 73 a, 73 h, 78 to 80). 



These nuclei are now ready to enter the synaptic or synizesis 

 stage, which immediately follows. They show essentially the 

 same characters in Oncopeltus, Lygaeus, Largus, and many other 

 Hemiptera ; but their composition is difficult to analyze precisely. 

 It is certain that the spireme is not continuous at this stage, for 

 free ends of the threads are readily seen ; but the number of threads 

 can not be determined. In general they show no trace of polariza- 

 tion, though in Lygaeus traces of such an arrangement are some- 

 times visible. Whether the threads branch or not is a very diffi- 

 cult question. At first sight they give the impression that they 

 do branch; and in my fourth 'Study' (on Pyrrhocoris) I described 

 them in fact as forming a ''net-like structure in which traces of a 

 spireme-like arrangement may sometimes be seen." The more 

 carefully one studies these nuclei, however, the more doubtful 

 this becomes. Certainly the threads may often be followed 



^ The mitotic transformation of the massive bodies is not however diagnostic 

 of the autosomes, for in some of the Orthoptera, as McClung and his successors 

 have shown, the X-chromosome is also converted into a closely convoluted thread 

 at a later period. I have some reason to suspect that the A'^-chromosome of Largus 

 may also consist of a very tightly convoluted thread in the earlier stages ; but there 

 is never any sign of its uncoiling, and in the later stages it appears homogeneous. 



