98 CHARLES V. MOKRILL. 



described them in Pyrrhocoris as forming the poles of tin- first 

 cleavage spindle ("Polkorperchen") and apparently considered 

 them to be archoplasmic masses. That he did not see an aster 

 in front of the male pronucleus nor an amphiaster at copulation, 

 in addition to these structures, is perhaps due to his methods of 

 technique. 



During the approach of the pronuclei the chromatin in each 

 becomes more and more condensed until the compact somewhat 

 elongated chromosomes appear. PI. II., c, the single example of 

 this stage found, shows the pronuclei of Archimerus, still slightly 

 separated. An indistinct aster appears at the right. In the 

 lower nucleus seven chromosomes of different sizes can be dis- 

 tinctly seen. The w-chromosome is missing and because of its 

 small size could not be identified in the next section. There 

 are no nucleoli in either pronucleus. 11 The chromosomes in the 

 upper nucleus are not yet fully condensed. The two pronuclei 

 are so nearly equal in volume that one cannot distinguish which 

 is male and which female even before copulation (PI. II., c). 

 It is apparent from a comparison of PI. II., b and c, that both 

 undergo a marked decrease in volume just before their nuclear 

 membranes fade out. PI. II., d, shows a late copulation stage or 

 prophase of the first cleavage spindle of Protenor in polar view. 

 The nuclear membranes have faded out but the chromosome 

 groups derived from each pronucleus are still separate. This 

 figure is obviously incomplete but it shows distinctly one reduced 

 group (at the right of the figure) in which all the chromosomes 

 appear, seven in number. Just as in the first oocyte division, the 

 idiochromosome is here recognizable by its relatively large size, 

 and does not in any way resemble a nucleolus. A next largest 

 chromosome and an w-chromosome also can be identified, the 

 remaining four being intermediate in size. The group at the left 

 of the figure shows the idiochromosome and three others, the 

 remaining chromosomes being too crowded in the next section 

 to identify. Since each group contains an idiochromosome it is 

 not possible to say which was derived from the egg nucleus and 

 which from a sperm of the class which bear this chromosome. 



"Stevens ('060, PI. IV., Fig. 119) has figured this stage in the "Goumi aphid" 

 where there are five chromosomes in each pronucleus, and, in the female, two 

 plasmosomes in addition. 



