372 



AN INTRODUCTION TO ZOOLOGY 



larger than the spermatocytes, and, indeed, in animals with heavily 

 yolked eggs, may become hundreds of times larger. They then 

 enter into a mitotic division ; the spireme concentrates in 

 synizesis, and from the chromatin mass reappear threads that 



Spermalogenes- 



Oogenesis 



Sperotitogoma < 



Primary 

 Spermaio'cytes 



Multiplication of Epithelial 

 Cells ( Spermat ogonia and 

 Oogonia) in [he Gonad 

 (Testis or Ovary) by ordinary 

 Somacic Mitosis 



Synapsis or Pairing xs! 

 of the Chromosomes V' 



1 1 



Reducing Division I \ 

 (Meiosis ) ; 5 



I r i \ 

 Male Gametes 



J4> Secondary Oocytts 

 (4f, and Polar Bodies 



^S Mature 0r* 

 & Polar Bodies 



& 



"Conjugation of / 



^eniiizatiotf Femai 



\ of 'Ovum/ y 



(^) 2>y^ OP Fertilized Ovuio 



Mature 



Segmentation of 

 the Zygote by 

 Ordinary Somatic 

 Mitosis 



(The figures indicate the numbers 

 of Chromosomes present) 



FIG. 126. Diagram of gametogenesis. From Dendy. 



are double as the result of synapsis, and they segment into 

 chromosomes. These chromosomes are bivalent, and so we have 

 only the haploid number present. An amphiaster is formed, 

 and the chromosomes become arranged upon the equatorial plate, 

 but instead of this taking place in the middle of the cell, it is right 



