STUDIES ON CHROMOSOMES 363 



answer the first two of these questions in the affirmative, while 

 the third remains unanswered. 



Stage b. It will be advantageous to consider this important 

 stage before that which precedes it, as there are doubts concern- 

 ing the latter; This stage and the following one are characteristic 

 of many Hemiptera and Orthoptera, and is seen also in the dra- 

 gon-fly; and some of these forms are much better adapted for its 

 critical study than are Oncopeltus and Lygaeus. 6 



In the latter forms numerous cysts in Stage b are seen in the 

 region between the spermatogonial cysts and the synaptic zone, 

 often abutting directly upon the former. For this reason I long 

 supposed this stage to follow immediately upon the last spermato- 

 gonial division, i.e., to be the last spermatogonial telophaso. Such 

 indeed is possibly the case in Largus, as already stated; but in 

 some other forms it is certainly separated from the telophase by 

 an intervening net-like stage. In Oncopeltus and Lj^gaeus Stage 

 b is characterized by rather small spheroidal nuclei in which may 

 be very distinctly seen a group of separate, more or less irregular, 

 massive chromatic bodies, the number of which is approximately, 

 in some cases exactly, equal to the diploid number of chromosomes 

 (figs. 50, 51, 71, 72). In preparations but slightly extracted 

 (after haematoxylin or saffranin) all these masses stain alike- 

 deep blue or red. Upon further extraction a very striking con- 

 trast appears between two of these bodies and the others, the 

 former retaining their deep color and having a fairly even contour, 

 while the latter become pale and are more or less irregular in shape. 

 As will be shown, the two dark bodies are the X- and F-chromo- 

 somes, which may be traced individually through all the succeed- 

 ing stages up to the spermatocyte-divisions. In Oncopeltus 

 they are spheroidal or ovoidal in shape and nearly equal in size 

 (figs. 50, 51). In Lygaeus the ^-chromosome is much larger 

 than the F, and always has the form of a more or less elongate 

 rod, which shows a good deal of variation, being sometimes quite 

 straight, sometimes curved in various ways (figs. 71, 72). In 



6 In my fourth 'Study' ('09 a) I gave a brief account of this stage in Pyrrhocoris, 

 illustrated by photographs, describing it as a ' spermatogonial post-phase, ' but did 

 not endeavor to work out the history of the autosomes. 



