BLACKMAN : THE SPERMATOGENESIS OF SCOLOPENDKA. 17 



of the lower types of Protozoa possess nuclei which are only masses of 

 chromatin, or karyosomes, lying free in the cytoplasm without any sur- 

 rounding memhrane whatever. That this is a strictly analogous body 

 in origin, structure, and function there can be no reasonable doubt. 



It is evident, then, that morphologically the karyosphere is at 

 this period the real nucleus of the cell. Whether at this time it also 

 functions as a nucleus in metabolism, my observations do not allow me 

 to decide. Howevei*, from the structural relations which exist between 

 the karyosphere, the nuclear vesicle, and the other organs of the cell, I 

 do believe we are not justified in drawing such a conclusion. We might 

 rather infer that at this time there is a division of labor, that certain 

 functions which generally pertain to the nucleus as a whole are localized 

 in a highly specialized portion of it, while the rest of the nucleus still 

 retains the powers not so delegated. 



We return now to the telophase of the last spermatogonium in order 

 to trace the development of the extra-nuclear structures of the cell. At 

 the time of the constriction of the cell wall the interzonal filaments, 

 drawn out between the separated chi'omatin plates, are forced together 

 at their equator so as to form a sheaf-like bundle (Figs. 7, 8). At this 

 time, also, the centrosomes are to be seen at the end of the cell farthest 

 from this regiou of constriction, surrounded by a mass of archoplasm 

 probably formed by the breaking down of the astral rays and mantle 

 fibres (Fig. 7). As the cell advances in development, the interzonal 

 filaments at the ends farthest from the point of constriction lose their 

 fibrillar character and break down into a loose mass of granules. In the 

 region of constriction the peripheral ones thicken into a number of dark 

 bodies, such as are characteristic of the spindle remnants of cells rich in 

 archoplasm, and form a baud encircling the remaining filaments. The 

 equatorial part of these remnants of the spindle is granular and contin- 

 ues so as long as any of it persists. 



Very soon after the stage represented in Figure 7, each pair of centro- 

 somes with their surrounding archoplasrn moves through the cytoplasm 

 around the mass of disintegrating chromosomes and finally comes to rest 

 at the ends of the remnants of the spindle (Figs. 9, 10). Here the 

 archoplasm surrounding the centrosomes becomes closely apposed to the 

 disintegrating archoplasm of the spindle remnants. The two masses 

 do not unite, however, but can be distinguished from each other through- 

 out all the subsequent changes (Figs. 12-16). From this time the 

 centrosome can be traced through the astonishing growth period, the 

 two subsequent divisions, the spermatid, and to its final position in 



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