STUDIES ON CHROMOSOMES 365 



more or less definitel}' polarized. In Anax and the Hemiptera, 

 on the other hand, they are of more less or rounded or irregular 

 form, and show no definite polarization. This is corelated with a 

 corresponding difference in the form and position of the spermato- 

 gonial anaphase-chromosomes. In the Orthoptera the latter are 

 in general rod-shaped, with their long axes parallel to the spindle- 

 axis; in Anax and the Hemiptera they are much shorter, often 

 rounded in form, and with their long axes (when distinguishable) 

 lying at right angles to the spindle-axis. The conditions described 

 above are occasionally varied b}^ the appearance of one or two 

 deep-staining bodies in addition to the sex-chromosomes, usually 

 of smaller size (cf. the photographs of Pyrrhocoris in my fourth 

 'Study'). Owing to their inconstancy I am uncertain as to their 

 nature. 



Whether all of these chromatic masses are chromosomes is a 

 question that probably can not be directly or certainly deter- 

 mined in the case of Oncopeltus and Lygaeus. We must rely 

 here upon indirect evidence. But there can be no doubt that two 

 of them are chromosomes, for the two deeply staining bodies of 

 Lygaeus and Oncopeltus 7nay be traced step by step, with no break 

 of continuity, into the two chromatic 'nucleoli' of the synizesis and 

 all succeeding stages, and thence throughout the growth-period into 

 the X- and Y -chromosomes of the maturation-divisions. Since the 

 paler bodies correspond in number to the spermatogonial num- 

 ber of autosomes, and since they undoubtedly give rise to the lep- 

 totene-threads that enter the synaptic stage, it is at least a fair 

 inference that they too are chromosomes, or are destined to 

 become such. 



Stage a. As stated above, I long supposed the stage just de- 

 scribed to follow immediately after the last spermatogonial divi- 

 sion; but it now seems certain that in Oncopeltus and Lygaeus, 

 as in the Orthoptera (Davis, op. cit.) it is preceded by one which 

 more nearly approaches the condition of a 'resting' nucleus. In 

 this stage only the sex-chromosomes can be clearly identified, 

 and there is reason to conclude that in a still earlier telophase 

 not even these can be distinguished. 



