454 



ROBERT W. HEGNER 



by Montgomery to be of cytoplasmic origin and is termed by him 

 a 'Sertoli cell determinant.' During the division of the ante- 

 penultimate spermatogonia the rod passes undivided into one 

 of the daughter cells; thus one-half of the penultimate sperma- 

 togonia possess a rod, the other half do not. Of the forty-nine 



Fig. 25 Stages in the formation of the Sertoli cell in man; (redrawn from 

 Montgomery, '11). A, spermatogonia containing granular inclusion (A") from 

 which 'Sertoli cell determinant' may arise. B, antepenultimate spermatogonium 

 showing rod (R) and idiozome (/). C, division of rod. D, a Sertoli cell con- 

 taining a divided rod (R) and two rodlets (r2). 



Fig. 26 Aequorea forskalea (redrawn from Haecker, '92). A, freshly laid 

 egg with germinal vesicle containing nucleolus. B, egg one-half hour after lay- 

 ing; nucleolus has escaped from nucleus. C, four-cell stage; nucleolus in one 

 blastomere. D, blastula; certain cells contain nucleolar-like inclusions (n). 



penultimate spermatogonia examined, twenty-four exhibited a 

 rod and twenty-five did not. This result has been confirmed 

 by von Winiwarter. When the rod-containing penultimate 

 spermatogonia divide there is a similar segregation of the rod in 

 one of the daughter cells, hence only one-fourth of the cells 

 resulting from the divisions of the antepenultimate spermatogonia 

 possess a rod. Of one hundred and forty-two cells of this genera- 



