174 



MONTGOMERY — A STUDY OP THE CHROMOSOMES 



In the monaster stage of the spermatogonia divisions can always be counted thirteen 

 chromatin segments on favorable pole views — i. c, in such cases where these elements 

 can be seen all in one plane, and where they are not too closely apposed to one another 

 (Figs. 108-110). Two of these elements are always distinguishable from the others by 

 their smaller size and rounded shape, and these arc the chromatin nucleoli (iV. 2) ; they 

 may lie close together (Fig. 110), but more usually are more separated in position (Figs. 

 108, 109). The remaining eleven elements, which are of large size and elongate form, 

 are chromosomes. There can be no doubt that this is the actual number of these chro- 

 mosomes, for no exceptions to it were found, and in fourteen clear cases from four different 

 testes the number eleven was obtained with great clearness ; these chromosomes are larger 

 than the spermatogonia chromosomes of any other Hemipteron examined. Sometimes 

 one or more of the chromosomes may show a slight transverse constriction, but this is not 

 a constant appearance. 



In the synapsis the two chromatin nucleoli derived from the spermatogonium unite 

 to form one bivalent one ; in the rest stage (which is very complete) of the spermatocyte 

 it is elongate (N. 3, Fig. Ill), peripheral in position and not attached to the true 

 nucleolus; the latter is larger (iV, Fig. Ill), frequently peripheral in position, and 

 sometimes two true nucleoli are present. 



During the synapsis stage ten of the eleven chromosomes join to form five bivalent 

 chromosomes, while the eleventh remains univalent, as will become evident from the 

 following description : 



In the first maturation division are found either seven chromatin elements or eight 

 chromatin elements; these two conditions may be described successively. 



When there are seven elements (Fig. 112 pole view of the monaster stage, Fig. 113 

 lateral view) one may always be distinguished by its smaller size and central position, 

 and by its history from the rest stage of the spermatocyte! to the stage under discussion 

 this is found to be the chromatin nucleolus (JV. e 2) ; this we have already learned to be 

 bivalent, and in Fig. 113 its univalent components are seen to be separating. The six 

 larger elements are chromosomes. Five of these, as Fig. 113 shows, are clearly dumbbell- 

 shaped and bivalent. The sixth, however (x), never shows a dumbbell shape before the 

 metakincsis, but is always distinguishable from the others by its oval form. From these 

 appearances we must conclude that this sixth chromosome is univalent — represents the 

 odd, eleventh, chromosome of the spermatogonia monaster stage, which had no mate with 

 which to unite during the following synapsis stage. It was in this species that I first 

 found spermatogonia with an uneven number of chromosomes, so that I first concluded 

 they must be abnormal cases, for heretofore in all objects the spermatogonia (normal) 

 number has been described as an even one; I immediately sectioned testes of other 



