igi2] SHARP— SPERMATOGENESIS IN EQUISETUM 113 



plant or animal group, it must not be forced upon those of all other 

 groups. Since homologies are not determined by function, there 

 is no necessity for expecting all of these organs to belong to the same 

 morphological category. It is in the algae that the blepharoplast 

 of plants at present stands most in need of elucidation. In the 

 bryophytes, pteridophytes, and gymnosperms there can now remain 

 no question that the blepharoplasts are all homologous structures, 

 and that they are, to use Ikeno's expression, " ontogenetically or 

 phylogenetically centrosomes." 



Summary 



mitoses in the spermatogenous tissue of Equi- 

 centrosomes, centrosoheres, or asters. 



minute 



appears in the cytoplasm near the nucleus in each of the cells of the 

 penultimate generation. This granule divides to two, which 

 become the blepharoplasts. 



3. The two blepharoplasts, each with its aster, diverge to oppo- 

 site poles of the nucleus. During the early stages of separation a 

 distinct central spindle develops, so that an amphiaster is present. 



form 



membrane 



become the achromatic portion of the karyokinetic figure. The 

 blepharoplasts occupy the poles. 



5. During the anaphases and telophases of karyokinesis the 

 blepharoplast enlarges, becomes vacuolate, and breaks up to a 

 number of pieces. After further fragmentation these unite to 

 the cilia-bearing thread. 



form 



6. In the metamorphosis of the spermatid the nucleus and 

 blepharoplast elongate spirally side by side, but have no connection 

 other than that afforded by the undifferentiated cytoplasm. 



7- The activities of the blepharoplast in Equisetum y taken 

 together with the behavior of recognized true centrosomes in 

 plants and analogous phenomena in animals, are believed to con- 

 stitute conclusive evidence in favor of the theory that the blepharo- 

 plasts of bryophytes, pteridophytes, and gymnosperms are derived 

 ontogeneticallv or Dhvloseneticallv from centrosomes. 



