. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. BLACKMAN: THE SPERMATOGENESIS OF SCOLOl''KA. 31 considered, this behavior is naturally expected. Owing to the compact manner in which the extremely line chromatin threads are aggregated in tiie karyosphere, only a few chromosomes can arise from it at one time, so that naturally those which are first formed are in more ad- vanced stages of development than those that appear later (Fig. 23). However, by the time the centrosomes are upon opposite sides of the nucleus and the nuclear membrane has begun to disintegrate
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. BLACKMAN: THE SPERMATOGENESIS OF SCOLOl''KA. 31 considered, this behavior is naturally expected. Owing to the compact manner in which the extremely line chromatin threads are aggregated in tiie karyosphere, only a few chromosomes can arise from it at one time, so that naturally those which are first formed are in more ad- vanced stages of development than those that appear later (Fig. 23). However, by the time the centrosomes are upon opposite sides of the nucleus and the nuclear membrane has begun to disintegrate, all of the chromosomes are in apparently the same stages (Figs. 29,30). All are dense, homogeneous structures, which take the stain with . â â 'V V'\- ':.. .;â¢" avidity and retain it strongly. While the other chromo- somes have been undergoing these changes in structure, ";⢠the accessory chromosome has also changed in shape. It has apparently at no time lost its homogeneous struc- ture, but that it has under- gone important changes is evident. It is no longer a spherical body, but now has the form of a rod, the ends of which are slightly notched (Figs. 29, 30, Fig. C). These Fig. C. Nucleus of first spermatocyte notches I believe indicate a during late prophase, showing various modi- longitudinal division. The neations in the shape of the chromosomes , ,.a. at this time. The accessory chromosome is accessory chromosome diners , . , .. , n . o mna J seen to be notched at the ends. Centrosomes from the other chromosomes with well-developed astral rays at opposite in shape and is evidently not poles of the nucleus. X 1,440 dia. of a tetrad nature. "When its origin is considered this difference in form is very easily explained, and is indeed exactly what would be expected. The other chromosomes are formed by a fusion of two of the spermatogonial chromosomes into one body during the telophase of the last mitosis of the division period. On the other hand the
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