BIGELOW: NUCLEAR CYCLE OF CONIONEMUS MURBACHII. 297 



becomes less and less dense, until it finally disappears altogether, leaving 

 the nucleus wholly translucent and apparently empty, except for the 

 reticulum and nucleolus, although we must assume that it is still filled 

 with some fluid substance. We cannot reach any very definite conclu- 

 sions as to the actual cause of the disappearance of the karyoplasm, yet, 

 from the radical nature of tli£ alteration, we must assume that it is 

 the visible expression of profound metabolic changes in the general con- 

 stitution of the nucleus. Furthermore, it is accompanied by one very 

 significant event : the karyosomes, previously basic, now reverse their 

 reaction and attain the acid character typical of chromatin in mitosis, 

 as is shown by their selecting the basic dye in the various acid-basic 

 mixtures. 



I may anticipate the following account by stating here that the same 

 two changes are likewise precisely contemporaneous in every other mi- 

 tosis which I have studied in Gonionemus. This is a very striking and 

 suggestive phenomenon ; but I am not prepared to couclude from it that 

 the reversal of the staining reaction of the karyosomes is a result of 

 the dissolution of the karyoplasm. It is perhaps more probable that 

 both are manifestations of the same underlying modifications of the 

 nuclear protoplasm. 



The reticulum now lies chiefly in a peripheral position, in contact 

 with the nuclear membrane, though many of its strands originate from 

 the substance of the nucleolus, which is still nearly central (Fig. 4). In 

 the latter structure, which has hitherto preserved the condition already 

 described for the " resting nucleus," marked changes now take place. 

 In the stage shown in Figure 5 it has lost its sharp contour, and bears 

 at its margin a series of irregular masses, which, to judge from their stain- 

 ing properties, are of chromatic nature, — one at the origin of each of 

 the linin strands. There is no doubt, I think, that these structures 

 have been derived from a partial disintegration of the deeply-staining 

 chromatic shell of the nucleolus, and that the central mass (Fig. 5), now 

 less deeply stained, is to be regarded as equivalent to a plasmosome. 

 Later stages in the disintegration of the nucleolus are most easily traced 

 on crushed cells, where the parts of the nucleus are separated. Such a 

 specimen, in which, however, only a few of the karyosomes are shown, 

 is represented in Figure 7. The nucleolus now consists of a central 

 vacuolated plasmosome, with six or seven separate chromatin masses 

 attached to its margin at the points of origin of as many linin strands. 

 At a slightly more advanced stage (Fig. 6) these masses become wholly 

 detached from the plasmosome, which then disappears. The clearness 



