THE SPERMATOGENESIS OF LEPIDOSIREN PAEADOXA. 43 
Fig. 3. — Spermatogonium, very early prophase. Chromatin blocks 
beginning to break up and spread out into bands. Corrosive-acetic. 
Fig. 4. — Spermatogonium, later prophase. The individual chromo- 
somes are in many cases clearly definable. Corrosive-acetic. 
Fig. 5. — Spermatogonium, fully formed spireme stage. The “spireme,” 
however, is plainly not continuous. Corrosive-acetic. 
Fig. 6. — Equatorial plate of one of the earlier generations of sperma- 
togonia. Corrosive-acetic. 
Fig. 7. — Equatorial plate of one of the later generations of spermato- 
gonia. ]Nos. 1-6 are each a single sharply bent chromosome. Corrosive- 
acetic. 
[In figs. 8-15 only the chromatin lying close under the nuclear mem- 
brane is shown.] 
Fig. 8. — Primary spermatocyte at end of growth period. Less than 
half the nucleus is contained in the section, so that its full diameter is 
not shown. Flemming. 
Fig. 9. — Leptotene stage. Flemming. 
Figs. 10-12. — Lep to- zygotene stage. In each case only the top of the 
nucleus is shown. Fig. 12, a polar view. All Flemming. 
Fig. 13. — Zygo-pachytene stage. Chromosomes arranged in bouquet 
form. Flemming. 
Fig. 14.— Pachytene stage, polar view. Corrosive-acetic. 
Fig. 15. — An unusually large pachytene nucleus. The reduced 
number of loops is present here (see p. 13). Corrosive-acetic. 
Fig. 16. — Polar view of strepsinema (diplonema). Synizesis is 
setting in. Most of the pachytene threads have split apart along 
their whole lengths (so far as can be seen) with the exception of their 
extreme ends, which remain united, thus forming long rings. In some 
places, however, the process of splitting can still be seen. One ring is 
cut through by the razor, showing two free ends. Flemming. 
Fig. 17. — Synizesis further advanced. Flemming. 
Figs. 18-23. — Stages showing breaking up of synizesis, shortening 
and thickening of chromosomes, complete separation of the ex-conju- 
gants and development of the transverse constriction in the univalents. 
Described on pp. 16-18. All nuclei, except fig. 21, untouched by 
the razor. All in 35—40 fx celloidin sections, mounted without dissolving 
out the celloidin. Fig. 20, two adjacent nuclei. In fig. 18 one of the 
elements is drawn separately. All corrosive-acetic. 
Fig. 24. — Immediately after disappearance of the nuclear membrane. 
Thirty-eight free, transversely constricted, univalent chromosomes. 
The nucleus is cut in two sections, both of which are shown. Flemming, 
paraffin section. 
