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HUBERT DANA GOODALE 



resulting in the formation of a well-defined blastoeoele (fig. 19). 

 In some blastulae the roof consists of only two layers of cells 

 while in others they are more numerous. The smaller eggs as a 

 rule appear to have the thicker roof. The fluid of the blasto- 

 eoele contains some substances, probably albuminous, which, on 

 fixing, appear as a white, rather flocculent mass. 



Often the cleavage planes cut only the more superficial portions 

 of the egg at first and only later cut through the interior. This 

 is shown in figs. 16, 17, and 18. The interior of the egg, lying 

 below the level of the equator, often is the last to be divided into 

 cells. 



Connected blastomeres 



It is not certain whether the connected blastomeres here de- 

 scribed, result from a non-development of the cell wall or from a 

 fusion of cells. Fig. 20 shows a vertical section of an egg which 



Figs. 20 and 21 



• 



externally appeared to be composed of sixteen cells. Fig. 21 

 shows the fifth section beyond. Corresponding parts of the egg 

 have been given the same letter. In fig. 20, a and b appear as 

 part of one cell, as do c and d, while / is connected to the general 

 yolk mass; e is a separate cell. In fig. 21, a, b, c, and d, are all 

 separate cells, while e now joins the yolk mass. Study of inter- 

 vening sections show that fig. 20 represents a true condition. 

 Careful study by means of camera drawings of all the sections 

 of two eggs showed that while twelve (possibly thirteen) nuclei 

 were present, only two completely separated parts existed. The 

 area between two cells lacking a cell-wall was often small, but was 

 definitely present. In other eggs, however, only slight evidences 

 of connected blastomeres were present. 



