162 MONTGOMERY A STUDY OF THE CHROMOSOMES 



in the monaster stage of the second division there are six univalent chromosomes, the 

 constrictions of which represent the reappearance of the longitudinal split (Fig. 20) ; 

 there are also in the same equatorial plate two non-constricted bodies of different volumes 

 which are not joined together. These are the chromatin nucleoli, which are regularly 

 halved in the first maturation metakinesis that is, they are the halves of univalent ones. 

 Thus the bodies marked N. 2 in Fig. 26 are the halves of those similarly marked in 

 Fig. 25. 



The second maturation division is equatorial, and the spermatid receives six chro- 

 mosomes, arranged in an outer circle around a single central chromatin nucleolus. 

 Accordingly in this second division one chromatin nucleolus passes undivided into one 

 daughter cell (spermatid), the other undivided into the other daughter cell. 



As in Euchistus variolarius, two follicles of the testis contain spermatocytes of a 

 much larger size than those in the four other follicles. 



, 3. Podisus spinosus Dall. 



Five testes of this species were studied. 



In the spermatogonic rest stage there are two small chromatin nucleoli, of more or 

 less rounded form, attached to the surface of a true nucleolus. 



In the spermatogonic monaster there are sixteen chromatin segments (PI. I, Fig. 

 27), two of which probably correspond to the chromatin nucleoli of the previous rest 

 stage. 



In the synapsis the fourteen chromosomes unite to form seven bivalent chromosomes. 

 The two chromatin nucleoli also come together to make one bivalent one ; in the growth 

 period of the spermatocytes (Fig. 28) the chromatin nucleolus lies close to the nuclear 

 membrane, and to its inner surface the true nucleolus is regularly attached. 



In the first maturation monaster there are eight chromatin elements, namely, seven . 

 chromosomes and one chromatin nucleolus, all bivalent and dumbbell-shaped on lateral 

 view ; the chromatin nucleolus has about the same volume as the smaller ones of the 

 chromosomes, and so cannot be distinguished from them with certainty. 



4. Mormidea lugens Fabr. 



Five testes were studied. 



In the rest stage of the spermatogonia there are two chromatin nucleoli (PL I, Fig. 

 30, N. 2}, which may be equal or unequal in size ; they may be attached together, which 

 is apparently the general rule, or may be separated, and one or both of them may be 

 apposed to the true nucleolus. 



In the spermatogonic monaster there are sixteen chromatin segments ; two of these 



