CYTOLOGY OF REPRODUCTION IN ANIMALS 



121 



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The Golgi material commonly forms a single large body, the acroblast, 

 situated near the posterior pole of the nucleus. 

 Most often the acroblast appears like a heavily 

 staining cup holding a less stainable material. 

 Soon it begins to move along the nucleus to the 

 anterior pole of the cell and then continues its 

 migration back along the other side, following a 

 path previously taken by the centrioles. At 

 some stage of this migration a small droplet of 

 matter appears to exude from the acroblast. 

 The droplet enlarges and organizes as the 

 acrosome, a specialized structure at the tip of the 

 spermatozoon, and a portion of it often differ- 

 entiates as a pointed 'perforatorium. What re- 

 mains of the acroblast, now known as the Golgi 

 remnant, moves backward along the developing 

 tail and is eventually lost from the cell in a mass 

 of protoplasm sloughed off at the close of spermio- 

 genesis. In species having no acroblast the 

 acrosomal material appears to come from numer- 

 ous small Golgi bodies. 



Conspicuous modifications of the spermatid 

 nucleus ordinarily appear after most of the 

 changes described above have been carried out. 

 Its chromatic matter gradually becomes con- 

 centrated, often against the nuclear membrane 

 in the anterior region, while its achromatic com- 

 ponent decreases in amount. Eventuall}^ the 

 nucleus becomes a dense and apparently homo- 

 geneous body closely united anteriorly with the 

 acrosome and posteriorly with one or both of the 

 centrioles, from which the axial filament extends. 

 The cytoplasm lengthens out along with the 

 axial filament and chondriosomal filament 

 sheaths. 



The mature spermatozoon, or male gamete, 

 consists typically of two main parts; the head, 

 comprising the nucleus, the acrosome, a surface 

 membrane, probably cytoplasmic in origin, and 

 occasionally other elements; and the tail, which 

 is made up of the axial filament, the filament 

 sheaths, and a small amount of residual cyto- 

 plasm. In many cases, notably mammalian 



Fig. 90. — Diagram of 

 typical mammalian sper- 

 matozoon, a, acrosome; n, 

 nucleus; c, c', centrioles and 

 their derivatives; w, cell 

 membrane; d, chondrioso- 

 mal matter; /, axial fila- 

 ment of tail; TO, middle 

 piece; p, principal piece of 

 tail; c, end piece of tail. 

 {After R. H. Bowen.) 



