STUDIES ON CHROMOSOMES 413 



univalent chromosome (X) of the same size. It is most inter- 

 esting to observe in Protenor the gradual emergence of the biva- 

 lents from the confused nuclear threadwork of Stage g. Early 

 stagesof the process are seen infigs. 115 to 117, which clearly demon- 

 strate (1) that the threads do not constitute a continuous spireme, 

 but are separate, (2) that they do not lie side by side in pairs to form 

 a diplotene, but are single and undivided. Figs. 118 and 119 show 

 two nuclei, only a little later than the preceding, in which all the bi- 

 valents are clearly seen and the large one is perfectly evident. It 

 is of course only now and then that a nucleus in this stage can be 

 found in which all the chromosomes are thus clearly distinguish- 

 able; the bivalents are still so extended and irregular as to present 

 a hopelessly confused picture in sections, and very frequently also 

 in smears. It is however my firm belief that the bivalent-figures, 

 intricately entangled though they are, are already quite distinct 

 at least as early as fig. 115, and I do not hesitate to accept this 

 as probable for the still earlier and more confused nuclei that 

 precede. 



From the latter part of Stage h (i.e., figs. 118, 119) every step 

 may readily be followed as the chromosomes continue to con- 

 dense, contract and increase in staining capacity. Of the innu- 

 merable nuclei showing these stages in my smear-preparations a 

 few are shown in figs. 120 to 131, and in photos. 40 to 51. As 

 these figures show, the typical number of separate chromatin- 

 bodies is eight, which may however be reduced to seven by the 

 coupling of the two smallest (w-chromosomes, figs. 124, 129, 

 130, photos. 45, 46, 48), or in certain rare abnormalities may be 

 increased to more than eight (fig. 128, photo. 43). Of these 

 eight, three are univalent, namely, the two smallest (m-chromo- 

 somes) and the large ^L-chromosomes, the latter always distin- 

 guishable by its more compact consistency, greater staining capac- 

 ity, rod-like form, and simple longitudinal split. 



The remaining five are the bivalent autosomes, which from the 

 beginning have the same forms as in Oncopeltus i.e., double 

 crosses, double V's, or longitudinally split rods which sooner or 

 later develop a transverse suture at their middle points and thus 

 are plainly seen to be of quadripartite nature. 



