126 THE DEVELOPMENT OF THE GAMETES OR SEX CELLS 



2. Basic Structure of the Definitive Sex Cell as It Starts to 



Mature or Differentiate into the Male Meiocyte (i.e., the 



Spermatocyte) or the Female Meiocyte (i.e., the Oocyte) 



The definitive sex cells of both sexes have a similar cytological structure. 

 The component parts are (fig. 68) : 



(1) nucleus, 



(2) investing cytoplasm, 



(3) idiosome, 



(4) Golgi substance, and 



(5) chondriosomes. 



The nucleus is vesicular and enlarged, and the nuclear network of chro- 

 matin may appear reticulated. A large nucleolus also may be visible. The 

 investing cytoplasm is clearer and less condensed in appearance than that 

 of ordinary cells. The idiosome (idiozome) is a rounded body of cytoplasm 

 which, in many animal species, takes the cytoplasmic stain more intensely 

 than the surrounding cytoplasm. Within the idiosome it is possible to demon- 

 strate the centrioles as paired granules in some species. Surrounding the 

 idiosome are various elements of the Golgi substance, and near both the 

 idiosome and Golgi elements, is a mass of chondriosomes (mitochondria) of 

 various sizes and shapes. The idiosome and its relationship with the Golgi 

 material, the mitochondria, and the centrioles varies considerably in different 

 species of animals. 



Much discussion has occurred concerning the exact nature of the idiosome. 

 Some investigators have been inclined to regard the surrounding Golgi sub- 

 stance as a part of the idiosome, although the central mass of cytoplasm con- 

 taining the centrioles is the "idiosome proper" of many authors (Bowen, '22). 

 Again, when the maturation divisions of the spermatocyte occur, the idiosome 

 and surrounding Golgi elements are broken up into small fragments. How- 

 ever, in the spermatids the Golgi pieces (dictyosomes) are brought together 

 once more to form a new idiosome-like structure, with the difference that the 

 latter "seems never to contain the centrioles" (Bowen, '22). It is, therefore, 

 advisable to regard the idiosome as being separated into its various com- 

 ponents during the maturation divisions of the spermatocyte and to view the 

 reassemblage of Golgi (dictyosomal) material in the spermatid as a different 

 structure entirely. This new structure of the spermatid is called the acroblast 

 (Bowen, '22; Leuchtenberger and Schrader, '50). (See fig. 68B.) A similar 

 breaking up of the idiosome occurs in oogenesis (fig. 68F, G). However, all 

 meiocytes do not possess a typical idiosome. This fact is demonstrated in 

 insect spermatocytes, where the idiosomal material is present as scattered 

 masses to each of which some Golgi substance is attached. 



The various features which enter into the structure of the definitive germ 



