38. 



fertilizecl, results in tiae formation of sub equal blastomeres, 

 figure 24. 



In the next cleavage, figure 25, tlie smaller blastomere 

 divides equally and the larger unequally. The eight celled 

 stage is formed by a cleavage at right angles to the two preced- 

 ing planes of cleavage, and the two sets of foiir cells each come 

 to lie in the position indicated by figure 26, the last division 

 being in the plane of the paper. 



One of these cells is considerably larger than the 

 other seven and, with the beginning of the next cleavage, begins 

 to be s«6i©:wfeat— ^u-s^so^adreii by Other cells, figure 27. The small 

 cell formed by the unequal division of this large cell, figure 28, 

 becomes a surface coll. What becomes of similar cells in later 

 divisions has not been determined, but, from sections, it appears 

 probable that the next small cell cut from the large cell, figure 

 29, crowds in over' the tip of the large cell and divides into 

 two, figure 37. 



Aboiit this time the outer cells, or at least part of 

 them, acquire cilia, figure 30, and the embryo rolls around on 

 the bottom of the dish. It finally rises to the surface an.d 

 swims freely. 



Just what internal changes take place during this in- 

 terval is rather hard to determine. Surface cells in the region 



