52 McCLUNG. 



only a single one is present, i. e., that only one chromosome be- 

 comes changed into a chromatin nucleolus : for in the synapsis, 

 when it may best be distinguished from the chromosomes, I have 

 never seen more than one long chromatin nucleolus. From the 

 synapsis on, the surface of the chromatin nucleolus gradually be- 

 comes smooth, so that its process of rounding off may be re- 

 garded as a mode of concentration of its substance. It finally 

 becomes homogeneous, quite different from the microsomal 

 chromosomes. 



29. " These phenomena show us the remarkable process of 

 the casting off of an entire chromosome, which is itself possibly 

 a mode of chromatin reduction ; and in the two spermatocytic 

 divisions we shall find that the chromatin nucleolus does not 

 again become a chromosome. . . . There are only two other 

 thinkable modes of origin of the chromatin nucleolus : i) that it 

 be extranuclear in origin, or 2) that it be a secretion of the 

 chromatin. 



30. " In the spermatocytes of Harpalns a chromatin nucleolus 

 has been seen by me, besides the true nucleolus ; and judging 

 from the observations of authors on various objects it would seem 

 that such a structure is generally characteristic of spermatocytes. 

 Thus Moore ('95) found in Elasmobranchs about the beginning 

 of the synapsis, ' a curious secondary nucleolus surrounded by a 

 vacuole, which, so far as I can ascertain, is in these fishes char- 

 acteristic of this change.' 



31. "Thus the true nucleolus passes from the periphery 

 toward the center of the nucleus, the chromatin nucleolus in the 

 reverse direction. 



32. " The chromatin nucleolus lies now in contact with the 

 nuclear membrane, and is rounded with the exception of that 

 side flattened against the nuclear membrane. 



33. " In the early prophases the chromatin nucleolus becomes 

 rounded, but at first retains its central clearer globule. At the 

 loose spireme stage it commences to grow smaller, at the same 

 time losing the central globule. . . . The decrease in size con- 

 tinues until the end of the loose spirem, when a dimension is at- 

 tained which is approximately uniform for the chromatin nucleoli 

 of all cells ; one or more of the smaller bodies, which arose as 



