THE CENTROSOME AND THE BLEP H AROPLAST 95 



sustain the homologies suggested by Belajeff. He pointed out that in 

 Marchantia centrosomes are present in all the spermatogenous divisions, 

 whereas in other liverworts they appear much later, and from this he 

 argued that the bryophytes show various stages in the elimination of the 

 centrosome. He strongly reasserted his belief that blepharoplasts are 

 centrosomes, and spoke of the "transformation of a centrosome into a 

 blepharoplast " in the development of a spermatid into a spermatozoid. 

 The ectoplasmic blepharoplasts of the algae were also held to be derived 

 from centrosomes. In the second paper he insisted less strongly upon the 

 morphological identity of all blepharoplasts, separating them into three 

 categories : (1) centrosomatic blepharoplasts, including those of the myxo- 

 mycetes, bryophytes, pteridophytes, and gymnosperms; (2) plasmoder- 

 mal blepharoplasts, including those of Chara and some Chlorophyceee ; 

 (3) nuclear blepharoplasts, found only in a few flagellates. 



For a further discussion of this question the student is referred to 

 the present author's papers on Equisetum and Marsilia. The main 

 conclusions reached may be stated in two extracts from the former paper : 



Although limited to a single mitosis in the antheridium, the blepharoplast 

 [of Equisetum} retains in its activities the most unmistakable evidences of a 

 centrosome nature, and at the same time shows a metamorphosis strikingly like 

 that in the cycads. In thus combining the main characteristics of true centro- 

 somes with the peculiar features of the most advanced blepharoplasts, it reveals 

 in its ntogeny an outline of the phylogeny of the blepharoplast as it is seen 

 developing through bryophytes, pteridophytes, and gymnosperms, from a func- 

 tional centrosome to a highly differentiated cilia-bearing organ with very few 

 centrosome resemblances. 



The activities of the blepharoplast in Equisetum [Marsilia, and Blasia], 

 taken together with the behavior of recognized true centrosomes in plants and 

 analogous j henomena in animals, are believed to constitute conclusive evidence 

 in favor of the theory that the blepharoplasts of bryophytes, pteridophytes, and 

 gymnosperms are derived ontogenetically or phylogenetically from centrosomes. 



Animals. The early researches of Moore (1895), Meves (1897, 1899), 

 Korff (1899), Paulmier (1899), and many other more recent investigators 

 have established the fact that the centrosome (or centrosomes) of the 

 animal spermatid plays an important role in the formation of the motor 

 apparatus of the spermatozoon, the axial filament of the tail growing out 

 directly from it (Fig. 35). Henneguy (1898) even saw flagella attached 

 to the centrosomes of the mitotic figure in the spermatocyte of an insect, 

 an observation which has been often repeated. Wilson (1900, p. 175) 

 concludes that "the facts give the strongest ground for the conclusion 

 that the formation of the spermatozoids agrees in its essential features 

 with that of the spermatozoa ..." and that the blepharoplast is 

 without doubt to be identified with the centrosome. 



