SPERMATOGENESIS OF SCUTIGERA FORCEPS. 169 



similarity in their structure and general appearance ; for while 

 the latter are very fine and delicate and do not appear to be sepa- 

 rate threads, but resemble rather mere elongations in the net- 

 work of the cytoplasm, the former are very heavy, stain an in- 

 tense black, and present the appearance of thick wires, the ends 

 of which may be distinctly seen lying free in the cytoplasm. 



At the opening of the metaphase (Fig. 17), the two centro- 

 somes lie at opposite poles of the cell, surrounded by the clear 

 transparent area and the radiating astral rays. The spindle lies 

 directly through the center of the cell, pointing toward the cen- 

 trosomes but not extending to them. It consists, of heavy, 

 intensely staining fibers. At their extremities these converge, 

 but do not unite. In the equatorial plate are the chromosomes, 

 nineteen in number, not lying in a circle on the periphery of the 

 spindle, but apparently scattered more or less irregularly in one 

 plane through the equatorial plate. Division and separation of 

 the chromosomes occur immediately, and the two groups soon 

 come to lie at opposite ends of the spindle fibers. 



As has been stated above, after the other chromatin has 

 entirely left the karyosphere, the accessory chromosome sepa- 

 rates from the nucleolar portion, which immediately breaks up 

 into numerous small particles. When the nuclear membrane 

 has disappeared, these particles are, of course, cast out into the 

 cytoplasm. They are not dispersed at once throughout the 

 whole cytoplasm, but in the metaphase, take up a fairly definite 

 position at each pole of the spindle proper, midway between cen- 

 trosome and equatorial plate. Thus, before the attractive force 

 of the centrosomes has succeeded in pulling apart the chromo- 

 somes, these particles already lie in the cytoplasm beyond the 

 extremities of the spindle fibers. Here they remain as long as 

 the centrosome is discernible, but after the latter disappears they 

 wander out throughout the cytoplasm and soon degenerate. 



Each centrosome, from the time it first becomes visible, con- 

 sists of two minute granules, surrounded by a transparent space 

 from which the short and delicate astral rays emerge (Figs. 12, 

 17). But at this period, shortly following the separation of 

 the chromosomes, each centrosome becomes surrounded by a 

 small, spherical-shaped region (Figs. 18, 19), which, when the 



