106 MONTi :oMKRY A STUDY OF THE CHROMOSOMES 



two chromatin nuclcoli found in tlie spermatogonia also unite to form one bivalent 

 chroniiitin nucleolus ; this is clearly bilobed in the earlier stages, but more rounded in the 

 later stages of the growth period of the spermatocytes (the larger of the bodies designated 

 N. 2 in Figs. 57, 58, G3) ; there is attached to it usually a small true nucleolus (Fig. ">Si. 

 Besides this large bivalent chromatin mieleolus there is also found in the spermatocytes. 

 most clearly seen in the rest stage, another much smaller one, of rounded form (the 

 smaller of the bodies marked N. 2 in Figs. 57, 58, 63) ; this is almost always apposed to 

 one of the true nucleoli (N), of which there are generally two large ones besides the 

 small one attached to the large chromatin nucleolus ; quite frequently the small chro- 

 matin nucleplus lies between the large one and a large true nucleolus (Fig. G3). This 

 small chromatin nucleolus is difficult to see in the synapsis stage, when the chromosomes 

 stain deeply, and since I was also unable to find it in the monaster stage of the sperma- 

 togonia, I could not determine whether it is bivalent or univalent or what its earlier 

 history is. It might well be present, however, in the spermatogonia, but be there so 

 minute as to escape detection. 



Pole views of the monaster stage of the first maturation division show sometimes only 

 seven chromatin segments (Fig. 62), and then these are six bivalent chromosomes and 

 the large bivalent chromatin nucleolus ; or they show eight segments (Figs. 59, 60), of 

 which the smallest is the small chromatin nucleolus of the growth period. That is to 

 say, in the equatorial plate there are always six bivalent chromosomes and the large 

 bivalent chromatin nucleolus, while the small chromatin nucleolus may be present or may 

 be absent. The lateral view of this stage given here (Fig. 61) shows seven large dumb- 

 bell-shaped elements, ol which six are chromosomes and one the bivalent chromatin 

 nucleolus though which one it would be hard to say, for all of these elements are of 

 approximately equal size and similar form ; while the smallest, eighth, element marked 

 N. 2 in this figure is the small chromatin nucleolus. When the latter persists into this 

 stage it appears to be halved in the following metakinesis. 



II. Trichopepla semivittata Say 



Four testes of this species were studied. 



In the nucleus of the resting spermatogonium are seen clearly two rounded chro- 

 matin nucleoli (N. 2, Fig. 64, PL II), of different volumes, one or both frequently 

 apposed to a larger true nucleolus (N). 



In the mouaster stage of the spermatogonia are found sixteen chromatin segments, 

 of which fourteen are elongate chromosomes, and two which are smaller and rounded are 

 the chromatin nucleoli (N. 2, Fig. 65), which here, as in the preceding rest stage, are 

 unequal in size. 



