OF THE GERM CELLS OF METAZOA. 



167 



In the following synapsis stage the fourteen chromosomes join to form seven bivalent 

 ones. The two chromatin nucleoli likewise unite to form one bivalent one, of which the 

 two components are unequal in size (Fig. 66, N. 2). In the telophase and rest stage of 

 the spermatocytes the chromatin nucleolus loses its earlier bipartite form and becomes 

 rounded (the larger of the bodies marked N. 2 in Fig. 67), and only occasionally is it 

 apposed to the larger true nucleolus {N). Sometimes the two chromatin nucleoli derived 

 from the spermatogonia do not unite together, but remain separated. During the growth 

 period, its later stages at least, can be seen in each nucleus tbree or four much smaller, 

 rounded bodies, which stain like the chromatin nucleoli ; some of them are often attached 

 to the surface of the true nucleolus (Fig. 67, the three smaller bodies designated N. 2). 

 There are certainly three of them and in some nuclei apparently four. I was unable to 

 determine with certainty these small cbromatin uucleoli in the rest and division stages of 

 the spermatogonia, though they might well be present there, but escape observation on 

 account of their minuteness. 



The monaster stage of the first maturation division (Figs. 68, 69) shows eight larger, 

 bivalent, dumbbell-shaped chromatin segments, of which seven are chromosomes and one 

 the large chromatin nucleolus (N. 2 of the figures). Of the seven chromosomes one is 

 always longer and more voluminous than the others (Figs. 68, 69), and is probably the 

 derivative of the two largest chromosomes found in the spermatogone divisions (Fig. 65). 

 Besides these eight large elements of the monaster stage of the reduction division there 

 may be seen on pole view usually one (Fig. 68), sometimes two much smaller granules, 

 which evidently represent the small chromatin nucleoli found in the growth period. 



SCUTELLARIIOJE. 



12. Eur >yg aster allernatus Say 



Three testes of this form were studied from individuals taken in July and August. 

 Each testis was filled with spermatocytes and spermatids, but contained no spermatogonia. 



In the spermatocyte in the rest stage one bilobed and hence probably bivalent 

 chromatin nucleolus (N. 2, Fig. 70, PI. II), which is peripheral in position and separated 

 from the usually smaller true nucleolus (iV). Sometimes the two components of this 

 chromatin nucleolus do not join together in the synapsis but remain separated through 

 the growth period. 



In the monaster stage of the first maturation division (Fig. 71, pole view) arc found 

 seven dumbbell-shaped (and hence probably bivalent) chromatin segments, of which the 

 smallest is undoubtedly the chromatin nucleolus (K 2), so that here there would be six 

 bivalent chromosomes. 



A. P. S. VOL. XX. V. 



