OF THE GERM CELLS OF MF.TAZOA. 



171 





of which, easily distinguishable from the others by their small size, are chromatin 

 nucleoli (N. 2). 



In the synapsis stage the twelve chromosomes unite to form six bivalent ones, and 

 the two chromatin nucleoli to form one bivalent one. In the late stages of the growth 

 period (Figs. 93, 94) the chromatin nucleolus (iV. 2) is rounded and peripheral in posi- 

 tion, and usually apposed to the true nucleolus ; even when they are separated the latter 

 is usually peripheral {N, Fig. 94) — an unusual position for it in spermatocytes of 

 Ifemiptera. 



In the monaster stage; of the first maturation division (Fig. 95) are seven elements, 

 namely, six bivalent chromosomes and one bivalent chromatin nucleolus (the smallest of 

 the seven elements, N. 2) ; all these are dumbbell-shaped on lateral view, and though 

 Fig. 95 is a pole view of the spindle two of its chromosomes are seen from the side. 



19. Ah/dus eurinus Say 



One testis of this species was studied. 



In the rest stage of the spermatogonia I could not determine chromatin nucleoli, 

 probably on account of their small size. 



Numerous monaster stages of spermatogonia were examined, and all showed thirteen 

 chromatin elements (PI. Ill, Fig. 96) ; two of these which are readily recognizable from 

 the others by their minute size are chromatin nucleoli (the two small granules shown in 

 Fig. 96) ; the eleven large elements are chromosomes, and have mostly an elongated 

 form. 



In the synapsis the two chromatin nucleoli unite to form one bivalent one, which in 

 the telophase of the spermatocytes (N. 2, Fig. 97) is relatively small, peripheral in posi- 

 tion, and quite frequently apposed to the larger true nucleolus (iV). Of the eleven uni- 

 valent chromosomes derived from the spermatogonium, ten unite to form five bivalent 

 pairs, while one (the eleventh) docs not unite with any of the others but remains uni- 

 valent. 



In the first maturation division are found seven chromatin elements (Fig. 98, pole 

 view) ; the smallest of these is bivalent, dumbbell-shaped, and is the chromatin nucleolus 

 (JY. 2) ; the six larger elements are chromosomes. Now a careful study of numerous 

 monaster stages seen on lateral view shows that only five of these chromosomes are dumb- 

 bell-shaped, and so bivalent on analogy with what is known for the other Hemiptera ; 

 while one of them is never dumbbell-shaped, approximately half the volume of the 

 others, and is univalent. Fig. 9!) is a, lateral view of the spindle of the first maturation 

 division, showing three of the live dumbbell-shaped chromosomes and (most to the right) 

 the univalent chromosome, in all cases where the chromosome plates of this stage can 





