34 



REPRODUCTIVE SYSTEM OF THE ADULT FROG 



Prophases of the heterotype division in the male Axolotl. (1) Nucleus of 

 spermogonium or young spermocyte. (2) Early leptotene. (3) Transition to 

 synaptene. (4) Synaptene with the double filaments converging toward the 

 centrosome. (5) Contraction figure. (6, 7) Pachytene. (8) Early diplotene. 

 (9) Later diplotene. (10) The heterotypic double chromosomes; the nuclear 

 membrane is disappearing. (Courtesy, Jenkinson: "Vertebrate Embryology," 

 Oxford, The Clarendon Press.) 



material, nor is there any permanent reduction at this stage in the 

 number of chromosomes. Their identity is lost only temporarily. This 

 is known as the pachytene stage. The members of each pair then 

 separate again. It must be remembered, however, that (a) the separa- 

 tion need not be along the original line of fusion and that (b) an 

 exchange of homologous sections of the chromosomes may occur 

 without any cytological evidence. In any case, the diploid number 

 of chromosomes reappears and this is then known as the diplotene 

 stage. 



