PLATE 4 



EXPLANATION OF FIGURES 



It is practically impossible to obtain a median section showing all of the details 

 of structure. It has therefore been necessary in certain figures to draw in one or 

 more structures (e.g., nucleolus or polar body nucleus) from adjacent sections. 

 This was done in figures 34 to 39. 



34 A median section showing the first maturation spindle, nucleolus, and 

 sperm. The latter w-as taken from the first section on the left. X 1167. 



35 A later stage, showing the three polar bodies and the female pronucleus. 

 X 1167. 



36 This section shows the cleavage nucleus (F.N.), the outer chromatin mass 

 of the first polar body division (Ai), and the polar nucleus (P), which has been 

 formed by a fusion of the inner chromosome group of the first polar body and the 

 second polar body. X 1167. 



37 A median section of the two-celled stage. X 1167. 



38 Median section of a four-celled stage. X 1167. 



39 A similar section of a slightly later stage. The nucleolus has broken up 

 and nearly surrounds the nucleus. The polar nucleus has undergone one division. 

 X 1167. 



40 The eight-celled stage. X 1167. 



41 Median section of a four teen-celled stage. The two blastomeres which 

 have received the nucleolar material lie at the top of the group of embryonic 

 cells. X 1167. 



42 A transverse section of a similar stage. X 1167. 



52 



