I/O GRACE MEDES. 



cells are stained but lightly by the iron-hsematoxylin, presents a 

 grayish appearance. In the center of this space, side by side, lie 

 two black granules. When the cell is stained a longer period 

 with the haematoxylin, this mass becomes very dark like the 

 centrosomes, and shows an irregular outline, appearing as if 

 formed by the fusing of the converging astral fibers. P. Bouin 

 ('03), in a recent paper under the title of " Centrosome et Centri- 

 ole " calls this entire structure, consisting of the two granules 

 and the surrounding sphere, the centrosome, and each individual 

 granule, a centriole ; using this method to prove that the centro- 

 some is not a permanent organ of the cell. But he seems to 

 have misunderstood the meaning which Boveri, the originator of 

 these terms, applied to them. The centrosome, as described by 

 the latter, is " Ein Korper, an den die Spharenradien direkt 

 herantreten, ist das Centrosome." He tells us that it is present 

 at all stages of cell-division, and divides to form the centers of 

 the daughter-cells. According to his description this may, in 

 the course of development, enlarge gradually, and become more 

 complex, until just preceding the metaphase it may take on the 

 form of a rather large, well-defined sphere in the center of which 

 one or more minute central granules or centrioles may appear. 

 Later, he adds as a test for distinguishing this enlarged centro- 

 some from the centrosphere, that through the latter astral rays 

 may be traced, while the former shows no such differentiation. 

 Bouin accepts Boveri's definition for the enlarged centrosome 

 during the metaphase, but rejects his definition of a centrosome 

 during the prophase and declares the two granules occurring at 

 that time to be the centrioles. In this manner he tries to prove 

 that the centrosome is not a permanent organ of the cell. That 

 his assertion is not valid in the case of Scutigcra is proved abso- 

 lutely by the fact that at no time during the existence of the 

 sphere surrounding the two granules does it appear sharply 

 defined from the astral rays, but these seem to traverse it and 

 radiate from the two central granules which are invariably dis- 

 cernible in those cells not too darkly stained. 



After the chromosomes have reached their destinations at the 

 extremities of the spindle-fibers (Fig. 19), the asters surrounding 

 the centrosomes fade away and the centrosomes themselves dis- 



