Blackman. — Spermatogenesis of Scolopendra. 



PLATE 2. 



All figures magnified 960 diameters. 



Fig. 2. Resting stage of spermatogonium of Scolopendra heros. All of the chroma- 

 tin is massed in one body, the karyosphere. The cell membrane is 

 much less distinct than the nuclear membrane. 



Fig. 3. Prophase of a spermatogonium. Chromatin in the form of 33 small 

 chromosomes. All of these except one, the accessory chromosome, are 

 granular. Centrosomes are now to be seen. 



Figs. 4, 5. Metaphase and anaphase, respectively, of the last spermatogonial 

 division. 



Fig. 6. Late anaphase of spermatogonium, as seen in a section oblique to the 

 axis of the spindle. 



Fig. 7. Telophase of last spermatogonial mitosis. The ordinary chromosomes 

 have begun to lengthen and become granular, while the accessory chro- 

 mosome still remains homogeneous. Centrosomes still in polar region 



of the cell. 



Fig. 8. Synapsis. The chromatin segments have lengthened still more. Acces- 

 sory chromosome unchanged. 



Figs. 9, 10. Synapsis completed. The chromatin segments, of the reduced num- 

 ber, are distributed more evenly throughout the nucleus, which is now 

 enclosed in a nuclear membrane. Centrosomes have migrated from the 

 poles. 



Fig. 11. Slightly later stage, showing the beginning of the formation of the kary- 

 osphere. Many of the chromosomes show evidence that they originated 

 by an end to end union of spermatogonial elements. 



Figs. 12-15. Later stages in the production of the karyosphere and in the growth 

 of the young spermatocyte. The centrosomes are still to be seen. The 

 remnants of the spindle of the last division still persist, and are con- 

 tinuous with the mantle of archoplasm surrounding the nucleus. 

 Figures 16-40 illustrate conditions of the first (primary) spermatocytes of the 



large type. 



Fig. 16. " Vesicle " stage of the large spermatocytes. All of the chromatin is 

 collected into the karyosphere, while the rest of the nucleus is less dense 

 than the cytoplasm. A mantle of archoplasm surrounds the nucleus, 

 and in a denser portion of this two centrosomes are visible. The per- 

 sisting remnants of the spindle are still seen. 



Fig. 17. Very early prophase of the large spermatocyte. The archoplasmic man- 

 tle has disappeared, and the character of the cytoplasm has altered. The 

 centrosomes have moved to the cell membrane, and are now migrating 

 apart along its surface. 



Fig. 18. Nucleus of a spermatocyte of Scolopendra heros, showing a karyosphere 

 similar to those characteristic of Scolopendra eubspinipes. 



