THE STRUCTURE OF CELLS 



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in question might have been looked for, and thus no little confusion 

 has been introduced into a subject already sufficiently bristling 

 with difficulty. But the cases of Acanthocystis (Schaudinn) and 

 of Actinosphaerium (R. Hertwig) show quite clearly that centro- 

 somes may, at least in the lower animals, be certainly differentiated 

 afresh in the cells from which they had previously been absent. 



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 f ^w^v&M 



c*< 

 *' 



FlG. 5. 



Acanthocystis aculeata. A and B, for- 

 mation of the centrosome from nuclear 

 constituents in swarm-spores. C, resting 

 cell. D, nuclear division preceding fission. 

 (After Schaudinn.) 



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The so-called Blepharoplast, which is associated with the male 

 reproductive cells of certain cycads and ferns, appears to present 

 very strong analogies with animal centrosomes, and yet the 

 blepharoplasts have not been seen in the antecedent cell -genera- 

 tions of the plants in which they occur, and hence they have 

 almost certainly been formed de now. On the whole, then, the 

 question as to the relative permanence of the centrosomes through 

 the series of ontogenetic cell-generations must be left an open one. 

 Certain facts are, however, known which conclusively prove that 

 centrosome-like structures can be formed in cells from which, under 



