GERM-CELL HISTORY IN THE BROOK LAMPREY 



11 



TABLE 1 

 A scheme representing in outline the different periods in the development of the germ 

 cells in vertebrates, and the terminology that might be etnployed when the sexes are 

 distinct from the beginning of development {columns I and II) and when the young 

 animal appears indifferent as to sex (cohimn III). See explanation in text 



PERIODS IN THE GERM- 

 CELL CYCLE 



1. Period of early se^ 

 regation 



GERM-CELL TERMINOLOGY 



Sex determined at or before fertilization 



Embryo and larva 

 male 



Primary sper- 

 matogonia 



3. First period of rest 



4. Period of secondary 

 division 



5. Period of matura- 



tion and growth 



a. Synapsis phase 



1. Leptotene 



2. Synaptene 



3. Pachytene 



4. Diplotene 



b. Growth phase 



1. Dictyate 



2. 1st matu- 



ration 

 division 



3. 2d matu- 



ration 

 division 



6. Period of cell meta- 



morphosis 



Embryo and larva 

 female 



Primary oogo- 

 nia 



2. Period of primary Primary sper- Primary oogo- 

 division matogonia nia 



Primary sper- 

 matogonia 



Secondary 

 spermato- 

 gonia 



Primary sper- 

 matocytes 



Spermatids 



Spermatozoa 



Primary oogo- 



Secondary 

 oogonia 



Primary 

 oocytes 



Ova 



Sex determined after fertili- 

 zation 



III 



Embryo and larva indifferent 



Stem cell 



Primordial germ cells 



Indifferent germ cells 



Indifferent germ-cells 



Male 



Primary 

 sperma- 

 tocytes 



Spermatids 



Spermato- 

 zoa 



Female 



Primary 

 oocytes 



Ova 



