474 WESLEY R. COE, 



Fig. 29. The germ-nuclei are fusing in a pseudopod-like process.. 

 The degenerating aster-fibres radiate in all directions from the vicinity 

 of the germ-nuclei, and do not have definite foci at any point. No 

 centrosomes can be found. 



Fig. 30. The germ-nuclei have fused. A pair of very minute, but 

 distinct centrosomes, with mere traces of developing asters, are seen in 

 a position exactly corresponding with that occupied by the sperm- 

 centrosomes and -asters in Fig. 26. The irregular fibres of the old 

 radiations of the sperm -asters are still to be seen, but they apparently 

 bear no relation to the new asters. 



Plate 21. 



Fig. 31. This stage follows that shown in Fig. 30. The germ- 

 nuclei have fused completely, and the cleavage-asters have begun to 

 develop. The remains of the old sperm-asters are seen throughout 

 the cell, as in Figs. 29 and 30, although they are much less distinct. 



Fig. 32. The cleavage - nucleus is elongated towards the young 

 cleavage-asters. The degenerating radiations of the sperm-asters are still 

 evident. The nuclear membrane has begun to dissolve away in the 

 immediate vicinity of the asters. 



Fig, 33. The cleavage-nucleus is still more elongated, and the 

 chromosomes are forming. All traces of the old radiations of the sperm- 

 asters have disappeared. A distinct centrosphere has been formed 

 about each centrosome. 



Fig. 34. The cleavage-spindle is nearly formed by the meeting of 

 fibres from opposite asters. The nuclear membrane still remains intact 

 above and below. The chromosomes lie in a zone midway between the 

 two asters. The yolk-globules are so deeply stained that they obscure 

 the cytoplasmic reticulum. It will be seen that the yolk is collecting 

 at the lower pole of the egg, while the upper pole is occupied by 

 protoplasm alone. 



Fig. 35. The rod-like chromosomes of the cleavage-spindle are 

 dividing. The centrospheres have increased greatly in size, and are 

 much less homogeneous than earlier. Each centrosphere contains two 

 minute centrosomes in its centre. 



Fig. 36. The asters at the ends of the spindle have increased in 

 size during the early anaphase. The fibres and granules left at the 

 equator of the spindle stain very deeply. The centrospheres continue 

 to increase in size. The two minute centrosomes contained in each 

 are no larger than in the previous figure. A slight indication of a 

 sort of central spindle is seen in the pair at the left-hand pole. 



Fig. 37. A pathological cleavage-spindle in the early anaphase. 

 To all appearances the egg-substance has been disturbed so as to cause 

 a partial rotation of the peripheral portions of the spindle from right 

 to left. The centrospheres have entirely disappeared, but the pair of 

 minute centrosomes at each pole of the spindle have retained their 

 former positions. 



