DAVIS: SPERMATOGENESIS. 117 



The apical cell seems not to occur in other groups of animals than 

 insects, although Lerat ( :05) has found peculiar cells in the ovary and 

 testis of Cyclops which seem to agree with it in some respects. 



Regarding the function of this cell there are in general two views: 

 one, that it is the progenitor of the germ cells; the other, that it has 

 nothing to do with the origin of the germ cells, but functions simply as a 

 supporting or nurse cell. Verson ('89, '91, '94) was one of the chief 

 exponents of the former view, holding that the other elements of 

 the testis are derived from the apical cell by amitotic division. Cholod- 

 kovsky formerly ('94) held the same view as to the origin of the tes- 

 ticular elements, but believed the divisions to be mitotic. His later 

 views are mentioned further on. More recently this view of the func- 

 tion of the apical cell has given way to the belief that it is a supporting 

 element; however, Verson's interpretation has been revived by Mun- 

 son (:06). This author believes that the apical cell (which he calls 

 the "grandmother stem cell") gives rise in some way to his "mother 

 branch cells," which immediately surround, and are in close connection 

 with the apical cell. These "mother branch cells" undergo repeated 

 mitotic divisions, the peripheral (distal) one of the daughter cells of 

 each division being budded off to form a "primary spermatogone," 

 which is the progenitor of all the spermatogonia of a given cyst, while 

 the other, or proximal one, remains connected with the apical cell to . 

 give rise later to successive primary spermatogonia. The cell which is 

 separated off (primary spermatogone) is accompanied by one or more 

 small nuclei, which later develop into cyst cells. These nuclei 

 Munson believes to be derived from very minute granules which occur 

 in the peripheral cytojilasm of the apical cell. They are a])parently 

 the same granules which have been interpreted by other investigators 

 as metabolic products. Just why Munson believes the spermatogonia 

 to be derived from the apical cell is not apparent, since he admits 

 that he has never seen this cell undergoing division, and in all cases 

 observed by him it differed greatly in appearance from the sperma- 

 togonia. 



Turning now to the other view, — that the apical cell is a support- 

 ing or nurse cell, — we find that this interpretation has been accepted 

 in some form or other by most authors. This view was held by 

 Ziegler und Vom Rath ('91), Toyama ('94), Erlanger ('96), La Valett'e 

 St. George ('97), Tichomirow ('98), Holmgren (:01), Griinberg (:03), 

 and recently Cholodkovsky (:05). Holmgren (:01) has traced deeply 

 staining granules from the nucleus into the surrounding cytoplasm. 

 He also found granules in the cytoplasm of the surrounding spermato- 



