10 Mary Blount. 



Chaet III. 



The next stage illustrated in the charts is that of eight (or perhaps 

 nine) cells, Chart III. The egg was taken from the shell gland at 

 4.45 a.m., about eight and three-fourths hours after fertilization. 

 The area of primary cleavage presents seven (or eight) large marginal 

 cells, which are continuous with each other at their outer borders, 

 and a smaller central cell which is limited on all sides superficially. 

 This cleavage pattern presents the beginning of the differentiation 

 of the primary area into central and marginal regions, as is more 

 completely illustrated in the sixteen-celled stage (see Fig. 48). The 

 accessory cleavage forms an incomplete circle at the inner margin 

 of the periblast (Chart III A). The marginal cells at the left and 

 posterior side of the blastodisc are definitely limited peripherally 

 by a line just inside of a zone of accessory cleavage. At the anterior 

 and right sides there are three gaps in the accessory cleavage, and 

 no peripheral limit to the marginal cells. In sections, sperm nuclei 

 are not found in this region. This condition of open marginal 

 cells will be referred to in the discussion of later stages, and par- 

 ticularly in the discussion of the periblast. The sperm nuclei have 

 increased in number as compared with the four-celled stage. Com- 

 pare Charts II B and III B. They occupy superficial positions in 

 the marginal periblast and many of them have migrated to the 

 peripheral edge of the zone which is recognized as the periblast in 

 surface view. They have also migrated deeper into the central peri- 

 blast and form a submarginal circle. 



Chart III C is a diagram of a central transverse section which is 

 shown in detail in Fig. 5. It is taken along the line X Y (Chart 

 III A) and the blastomeres are indicated by corresponding letters 

 in the two figures. 



ClIAllT IV. 



The next chart (IV) presents the last stage in the nuiltiplication 

 of the sperm nuclei in an egg of about thirty-two cells. The surface 

 view (A) is incompletely represented. The blastomeres seemed to show 

 shrinkage in the salt solution and the egg was hurried on into the 

 killing fluid without taking time to complete the drawing. Enough 



