424 ' BOTANICAL GAZETTE [November 



During anaphase a new centrosome appears at each spindle pole, 

 exactly as in the second mitosis, and behaves in a wholly similar 

 fashion in the subsequent stages. When first discernible it is 

 extremely minute (fig. 25), but very rapidly becomes larger (fig. 26). 

 This formation of new centrosomes after the failure of the old ones 

 is a feature of considerable interest, and will be touched upon again 

 in the discussion. 



The division of the centrosome occurs during the telophases, but 

 not always at exactly the same stage, as figs. 27 and 28 show. In 

 fig. 27 the lower centrosome is elongating and the upper one begin- 

 ning to constrict. In fig. 28 the lower one is still spherical, while the 



upper one is almost completely divided. 



Fourth spermatogenous mitosis. — In the interval between the 

 third and fourth mitoses the centrosomes gradually move apart 

 (figs. 29-31). In view of the role which they are to play, they may 

 now be called the blepharoplasts. As they diverge, a delicate cen- 

 tral spindle remains between them. The radiations on the side 

 toward the nucleus become stronger, and at the stage shown in 

 fig. 31 form two conspicuous cones of spindle fibers with the ble- 

 pharoplasts at their apices. The rays extending in other direc- 

 tions are not so well developed as in the previous mitoses. 



A marked change now begins in the blepharoplasts. They en- 

 large, develop one or more internal vacuoles, and become irregular 

 in outline (figs. 31, 32). At late anaphase this process has gone on 

 still farther (fig. 33), and at telophase they may be seen breaking 

 up to several irregular pieces (fig. 34). 



Metamorphosis of the spermatid. — The transformation of the 

 spermatid into the spermatozoid seems to take place rather rapidly. 

 The fragmentation of the blepharoplast, begun during the telo- 

 phase of the last mitosis, continues until a considerable group of 

 pieces has accumulated (fig. 35). These soon take the form of an 

 irregular, lumpy rod, which lies close to the nucleus or against it 

 (fig. 36). A later stage is shown in fig. 37; in this cell, which is 

 noticeably larger than those of figs. 35 and 36, the nucleus has begun 

 to undergo a change in shape which will finally result in the spiral 

 form of the sperm, and the blepharoplast, in close union with it, has 

 formed nearly one complete turn. 



