.ii«»~« -•;••- 



Figure 2. — The stages of jack mackerel egg development. 



Stage I: Unfertilized eggs or fertilized eggs prior to cell division. 



Stage II: Begins when the first cell becomes visible on the yolk and 

 ends at the completion of the blastodisc formation (about 

 256 cell stage). 



Stage III: Starts at the completion of blastodisc formation and is 



terminated when the germ ring has migrated to its greatest 

 diameter (halfway up the egg). 



Stage IV: Begins as the germ ring moves upward over the greatest 

 diameter and stops when the germ ring lies over the oil 

 globule, prior to blastopore closure. 



Stage V: Begins at blastopore closure and terminates when the tail 

 starts to^separate from the yolk. 



Stage VI: Begins when the tail bud comes free of the yolk and stops 

 when the posterior eighth of the body is free of the yolk. 



Stage VII: Begins when the posterior eighth of the body is free of 



the yolk and stops when the posterior quarter of the body 

 is free of the yolk. 



Stage VIII: Begins when the posterior quarter of the body is free of 

 the yolk, and ends as the tip of the tail approaches the 

 chin. The tail portion of the embryo begins to rotate 

 out of the embryonic plane and the fin-fold is moderately 

 wide. 



Stage IX: Is characterized by the tip of the tail laterally approaching 



the head. The oil globule comes to lie in the anterio-vertical 

 portion of the yolk sac. The fin-fold is wide and fully formed, 

 At the termination of the stage, the embryo hatches. 



Disintegrate: All jack mackerel eggs whose internal structure is such that 

 staging is impossible fall into this category. 



