360 EDMUND B. WILSON 



like structure, and for a short time their boundaries can not cer- 

 tainly be distinguished. In the latter part of this stage the X- 

 and F-chromosomes become clearly recognizable as compact, 

 deeply staining bodies; but in the earlier stages they too seem to 

 be in a diffused condition. This stage, of short duration, corre- 

 sponds to Davis's 'Stage a' in the Orthoptera ('08), and probably 

 may be compared to the 'resting stage' that has been described 

 as following the last diploid division in many other forms. 



b. (Figs. 50 to 51.) Post-spermatogonial nuclei of somewhat 

 larger size, in which the chromatin appears in the form of separate, 

 massive bodies, approximately equal in number to the chromo- 

 somes of the diploid groups. Two of these, of more even contour 

 and staining more deeply, are now recognizable as the sex-chro- 

 mosomes. The other masses are more or le'ss irregular in form, 

 often ragged in texture, and stain more lightly. 



c. (Figs. 52 to 55.) The lightly staining masses are in this 

 stage transformed into delicate, closely coiled or convoluted 

 threads, while the sex-chromosomes retain their massive form, 

 and are thus rendered very conspicuous. In the latter part of 

 this stage the fine threads are seen uncoiling or unravelling from 

 the massive bodies to form the leptotene-threads of the following 

 stage. 



d. (Figs. 56 to 59.) The pre-synaptic leptotene. The auto- 

 somes now have the form of long delicate threads, while the sex- 

 chromosomes retain their massive form as 'chromosome-nucleoli.' 



e. The synaptic stage or synizesis (figs. 60 to 61). The threads 

 are now much thicker, stain more deeply, and are closely convo- 

 luted in a contraction-figure or synizesis. A plasmasome can 

 sometimes be distinguished at this time, but is usually first seen 

 in the ensuing stage. 



f. Post-synaptic spireme (pachytene, diplotene, figs. 62 to 

 65) . Separate thick threads are now again spread through the 

 nucleus, approximately of the haploid number, and in the latter 

 part of the period longitudinally divided. The plasmasome is 

 now nearly always present, though rather small. 



g. The diffuse or confused stage (figs. 66 to 67). The double 

 segmented spireme disappears from view, giving rise to a rather 



