9 



give rise to two different reproductive types of cell ex- 

 pressive of difference of sex. In certain animals both 

 types occur in the same individual (hermaphroditism) ; 

 but in most of the higher forms the sexes are separate, 

 and the sex-cells are produced in special reproductive 

 organs or jgonajjs (testis in the male, ovary in the female) 

 formed from the germinal epithelium. Both types are 

 termed gametes because they conjugate (to form the 

 zygote). The male gamete (microgamete or spermatozoon) 

 is very" small, very active, and produced in great numbers. 

 The female gamete (macrogamete or ovum) is stored with 

 food- yolk for the future embryo and is proportionately 

 larger ; it is not active and is produced in smaller 

 numbersj 



Write a short Account of Spermatogenesis and Oogenesis, 

 or the History of the Production and Maturation 

 of the Male and Female Gametes in the higher 

 Animals or Metazoa. 



The primitive male germ cell becomes a mother-sperm- 

 cell or spermatogonium, which by ordinary mitotic division 

 becomes a spermatocyte, which then undergoes meiotic 

 or reducing division (meiosis). Each spermatocyte divides 

 into two, each of these again divides into two, and thus 

 four spermatozoa are formed, 



The history of the female gamete (oogenesis or maturation 

 of the ovum) is at first similar to that of the male, and 

 the resulting oocyte (immature ovum) undergoes meiotic 

 or reduction division (meiosis). This does not, however, 

 result in an equal division of cell substance, but only in 

 the extrusion of a small portion known as a polar body. 

 A further (but ordinary mitotic) division results in the 

 extrusion of a second polar body ; and the first polar body 

 often divides into two. In this way four potential ova 

 are formed. Three of these (the polar bodies) come to 

 nothing, but the fourth is the mature ovum or egg, now 

 ready for fertilisation by union with a spermatozoon. 



