46 FISHERIES OF THE UNITED STATES. 



Figures 8, 9, 10, 11, 12, and 13, the changes during the second 

 period of rest ; Figures 14, 15, and 16, those which take place dur- 

 ing the second period of activity ; 17, 18, and 19, those which take 

 place during the third period of rest ; 20 and 21, during the third 

 period of activity ; 22, during the fourth period of activity ; 23, 

 during the fifth period of activity, and the remaining figures 

 show more widely sejiarated stages. In all the figures of seg- 

 mentation, excejjt 29, 30, and 31, the formative pole is above and 

 the nutritive pole helow. 



Figure 1. — Eggs two hours and seven minutes after fertiliza- 

 tion. It is now perfectly spherical, with an external membrane, 

 and the germinative vesicle is not visible. 



Figui'e 2. — The same egg two minutes later. It is now elon- 

 gated; one end is wider than the other, and a transparent area 

 at the broad end marks the point where the polar globules are 

 about to appear. At the opposite end the external membrane is 

 wrinkled by waves which run from the nutritive towards the 

 formative pole in rapid succession for about fifteen seconds. 



Figure 3. — The same egg two minutes later. 



Figure 4. — The same egg two niinutea later. The yolk has be- 

 come pear-shaped. The polar globule has appeared at the form- 

 ative pole, in the middle of the broad end of the pear, and the 

 nutritive end of the egg is now less granular than the formative 

 end. 



Figure 5. — The same egg two minutes later. Three et^uidistant 

 furrows have made their appearance, separating it into' a single 

 mass at the nutritive pole, and two at the .formatiA'e pole. At 

 this stage the three masses are about equal in size. 



Figure 6. — The same egg two minutes later. The first micro- 

 mere, c, is now perfectly separated, and smaller than the second, 

 h, and each is smaller than the macromere, a. 



Figure 7. — The same egg one minute later. Both micromeres 

 are separated and are spherical, as is also the macromere. This 

 stage ends the first period of activity. 



Figure 8. — The same egg forty-five seconds later. The two mi- 

 cromeres have begun to fuse with each other, and the second mi- 

 cromere, h, is also jiartially fused with the macromere, a. 



Figure 9. — The same egg one minute later. The first micro- 

 mere, c, has also begun to unite with the macromere. 



Figure 10. — The same egg one minute later. The line between 

 the second micromere and macromere has disapjieared, and the 

 first micromere, c, now projects from one end of the elongated 

 mass formed by the union of the spherules a and b. 



Figure 11. — The same egg thi'ee miniites later. The fusion of 

 a and h is now complete, and a large transparent vesicle is now 

 visible in the first micromere, c, and another in the compound 

 mass, ah. 



Figure 12. — The same egg two minutes and thirty seconds later. 



Figure 13. — Another egg, about two minutes later. This is the 

 true resting stage, at the end of the second period of rest. The 

 two vesicles have become irregular. The remains of an external 

 membrane adhere to one side of the egg. 



Figure 14. — The same egg seven minutes later than Figure 13. 

 The compound mass, a and i, is elongated, the first micromere, c, 

 is well defined, and waves travel from the nutritive towards the 

 formative ends of the two masses. Two segmentation nuclei oc- 



