The Spermatogenesis in Pentatoma up to the Formation of the Spermatid. 23 



with the nuclear membrane (Figs. 55—68); but at the end of the 

 synapsis it gradually takes up a more peripheral position, so that 

 usually during the synapsis, and always in the telophase and rest, 

 it is closely apposed to the nuclear membrane. It cannot be seen in 

 all cells in the synapsis, because it is frequently hidden in the mass 

 of chromosomes (Figs. 60, 66, 69); in other cases one or both ends 

 of it are found projecting out from the surface of this mass (Figs. 61, 

 64). But in most cells in the synapsis it occurs in the nuclear cavity 

 apart from the chromosomes. In such cases it is found to be usually 

 rod-shaped, often more or less curved, occasionally even lobular 

 (Figs. 67, 68); but so great is its irregularity in form, that in no 

 two cases does it have exactly the same shape. Throughout the 

 synapsis the chromosomes stain an intense violet, so that by strong, 

 obliquely-reflected light the chromatin nucleolus may be readily detected 

 by its deep red color. In the colored figures given to represent these 

 relations the coloration of the chromatin nucleolus is represented as 

 seen on thin section ; when it is viewed in its entirety, not on section, 

 the refraction of the light produced by its rounded surface gives it a 

 darker color *). Afterwards it either gradually shortens up into the 

 ultimate spherical form; or first becomes constricted at one or more 

 points on its surface, showing then a more or less beaded appearance 

 (Figs. 63, 71), and then, by division at these points, breaks into a 

 number of unequal fragments, each of the latter subsequently rounding 

 otf (Fig. 62). The various stages of such divisions are found in abund- 

 ance, and this is undoubtedly the mode of origin of the several 

 chromatin nucleoli found in a number of cells in the rest stage. But 

 it is most probable that at first only a single one is present, i. e. that 

 only one chromosome becomes 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 becomes smooth, so that its process of rounding 

 off may be regarded as a mode of concentration of its substance. It 

 finally becomes homogeneous, quite different from the microsomal 

 chromosomes. The stages of its metamorphosis do not strictly coincide 

 with given stages in the arrangement of the chromatin ; thus I have 

 noticed that the primitive irregular shape of the chiomatin nucleolus 

 sometimes persists as late as the postsynapsis. 



1) These observations were made with a chromatic lens, but sub- 

 sequent studies with apochromatic lenses gave the same color reactions. 



