476 R. M. PACE. 



Fig. 35. — Section of the {germinal vesicle at a stage slit^litly later than that 

 shown in fig. 34. The nucleolus has become relatively very large, the 

 chromatin network is thicker, and the substance between the meshes stains 

 still more deeply than at previous stages. X 650. 



Fig. 36. — Section of the germinal vesicle in a mature egg before the 

 formation of the polar bodies has taken place. The germinal vesicle has 

 decreased in relative size and has assumed an amoeboid form. All trace of the 

 chromatic network has vanished. X 650. 



Figs. 37-42. — Series illustrating the primitive cleavage of the egg. x 65. 



Fig. 43. — The segmenting egg at the four-cell stage. X 90. 



Fig. 44. — The segmenting eg^ at the eight-cell stage. Lateral view. 

 X 90. 



Fig. 45. — The segmenting egg at the twelve-cell stage. X 90. 

 (a) Lateral view, (d) Aboral view. 



Fig. 46. — Oral view in optical section of the larva at the twelve-cell stage, 

 showing the formation of spindles in the four oral cells prior to the division 

 which gives rise to eight oral cells. X 400. 



Fig. 47. — Larva at the sixteen-cell stage. X 90. 



(a) Oral view, (b) Lateral view, (c) Aboral view. 



Fig. 48. — Oral view of the larva at the sixteen-cell stage, showing tlie 

 formation of spindles in the four central oral cells prior to tlicir division to 

 form four new oral cells of the sixth generation. X 180. 



Fig. 49. — Larva at the twenty-cell stage. X 90. 



{a) Oral view, (b) Lateral view, (c) Aboral view. The four large 

 oral cells are of the sixth generation ; of the eight surrounding cells, four 

 belong to the fifth and four to the sixth generation. 

 Fig. 50. — Larva at the thirty-two cell stage. X 90. 



(a) Oral view, (b) Lateral view, (c) Aboral view. 



PLATE 24. 



Fig. 51.— Section of an egg in which the first polar body has been formed and 

 the second is in process of formation ; the first polar body lies outside the 

 egg. X 250. 



Fig. 52. — Section of a larva at the four-cell stage showing the formation of 

 the nuclear spindles prior to the division to form the eight-cell stage, x 225. 



Fig. 53. — Longitudinal section of the larva at the twenty-cell stage, x 225. 



Fig. 54 «. — Transverse section of the larva at the twenty-cell stage, showing 

 the formation of nuclear spindles in the aboral cells A|, C|, prior to division. 

 The four oral cells belong to the sixth generation. X 225. 



