174 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Skr. 



connection with the nucleus. They can no longer be 

 traced through the perikaryoplasm. Where the outer 

 reticulum abuts on the perikaryoplasm the meshes of the 

 former are so compressed as to give the impression of a 

 loose membrane. 



These two constituents of the cytoplasm not only differ 

 from one another as regards their structure but their staining 

 properties stand in great contrast. While the outer reticu- 

 lum stains a light or gray-blue with the gentian violet, the 

 perikaryoplasm stains a decided orange with the orange G. 

 The entire cytoplasm thus presents the appearance of two 

 distinct and sharply differentiated zones, differing from one 

 another as regards structure and staining properties. These 

 zones are seen in fig. 5. 



In case it should be thought that this is due to artifact, it 

 might be well to state here that a large number of living 

 cells were examined, and this striking differentiation of the 

 cytoplasm and the ring of spherical bodies, together with 

 the threads of the outer reticulum, could be readily seen. 

 This, in the writer's opinion, is sufficient evidence to prove 

 that the phenomenon is a normal one. There seems little 

 doubt that it is the first step towards the formation of the 

 spindle. 



In fig. 6 we see the first indication of the breaking down 

 of the nuclear wall. It evidently does not break down all 

 at once. It commences to do so at one or more points 

 where it becomes lost in a network which is now developed 

 out of the linin and perikaryoplasm. Figs. 6-8 show stages 

 in the breaking down of the nuclear membrane. It will 

 be seen from these figures that the perikaryoplasm, 

 where it is in the immediate vicinity of the breaks in 

 the nuclear wall, is now undergoing a change. The linin 

 has lost its lumpy appearance and now appears as fine, 

 delicate threads (fig. 6) which are in direct communication 

 with the perikaryoplasm. The latter is losing its granular 

 nature in these places and is taking on the form of a net- 

 work. In fig. 8 we see this network taking on a very 

 definite form. It no longer stains orange, like the 



