SPEKMATOGENESIS OF SCUTIGERA FORCEPS. 1 6/ 



others into the nuclear area. At first it may be distinguished 

 from them by its small, regular form and intense stain. But 

 when the others have contracted into the dumb-bell shape, they 

 are of uniform size with the accessory, stain similarly and thus 

 are indistinguishable from it. But that this element assumes its 

 position also in the equatorial area at the time of the metaphase 

 is shown by the fact that there are nineteen chromosomes now 

 present whereas but eighteen chromatin segments could be seen 

 emerging from the karyosphere, and but eighteen tetrads ob- 

 served later. 



As the cell approaches the metaphase, the karyoplasm con- 

 tinues to break down, and assumes more and more the appear- 

 ance of separate threads. At first these are wavy and irregular 

 and often much branched, being, in fact, but segments of the 

 linin reticulum. Later, however, at the time of the disappear- 

 ance of the nuclear membrane, they straighten and lie like single 

 threads in the cytoplasm. The centrosomes, meanwhile, have 

 remained in the cytoplasm at some distance from the nuclear 

 membrane. As this fades away, the threads formed from the 

 network of the nucleus stretch from one centrosome to the 

 other, and, losing their granular consistency, take on the form of 

 distinct, definite fibers. 



Preceding the breaking down of the nuclear membrane, the 

 nucleus often wanders from its central position in the cell and 

 assumes a position near the cell-wall. Bouin ('01), in Geop/iilns 

 lincaris, describes two methods of cell-division ; one " division 

 axiale," which represents the usual type where the centrosomes 

 lie at opposite poles of the cell with the spindle between ; the 

 other, "division laterale," in which the spindle lies near the 

 periphery and is often tangent to the cell-wall. In the latter 

 case, he says : " Les corpuscules centraux et les spheres s'at- 

 tachent centre la face interne de la membrane cellulaire, la ligne 

 que les reunit est souvent d'une longueur moindre que le grand 

 diametre de la cellule . . . Les extremites du fuseau peuvent se 

 trouver si voisine des centres cinetiques qu'elles paraissent se 

 continuer avec la substance de ces formations." 



But although cells answering to this description are often to be 

 found in Scntigera before the metaphase, there does not seem to 



