620 BULLETIN OF THE 



Fig. 34. The clear spot has moved to near the centre of the egg ; the equatorial 

 zone is less distinct. 



Fig. 35. The first segmentation furrow has already extended to the vegetative 

 pole. 



Figs. 36-38. Three views of the same egg, at 8:10, 9:04, and 9:15 o'clock. 



Fig. 36. Male and female pronuclei, and equatorial clear zone {pz) visible, the 

 latter intermediate in prominence between that of Figs. 33 and 34. 



Fig. 37. Beginning of the first segmentation of the yolk. The pronuclear struc- 

 tures have disappeared, and the oval spots, from the position of the egg, partly cover 

 each other. 



Fig. 38. Near the close of the first segmentation. 



PLATE II. 



Fig. 39. Optical section of an egg, showing the first archiamphiaster, and pe- 

 ripheral clear areas in the yolk. 



Fig. 40. Optical section of an egg and first polar globule, with lateral zones of 

 thickenings, prominent interzonal filaments, and possible indications of an amoeboid 

 character of the yolk at the animal pole. 



Fig. 41, Surface view of the polar globule of the same. 



Fig. 42, View of same globule, the optical axis coinciding with the primary (ani- 

 mal) radius of the egg. It shows the annular arrangement of the spindle thicken- 

 ings, and the outline of the pedicel. 



Fig. 43. First archiamphiaster. The external aster causes a protuberance at the 

 surface of the yolk, and exhibits a highly refractive body at the centre of radiation. 

 Nuclear spindle inconspicuous ; equatorial thickenings not prominent. 



Fig. 44. Section of an egg just before the first segmentation. The plane of sec- 

 tion is parallel with the axis of the spindle. About one third of the spindle was cut 

 away by the section preceding the one here represented. A highly refractive spherical 

 body occupies the centre of each of the astral areas, and the thickenings of the spindle 

 fibres are arranged in two closely approximated parallel zones. 



Fig. 45. First archiamphiaster at the time the rays of the external aster attain 

 the surface of the yolk. The external aster is more sharply outlined than the in- 

 ternal. The first maturation spindle presents only a single (equatorial) zone of fibre 

 thickenings. The flattened appearance of the animal pole is probably due to the 

 resting of the yolk on that pole during its preparation, and while still incompletely 

 hardened. 



Fig. 46. Equatorial optical section of the same; the spindle thickenings are 

 projected, and exhibit the usual annular arrangement. 



Fig. 47. External aster of same; the optical axis coinciding with the axis of 

 the spindle. The rays have a spiral course. 



Fig. 48. The first archiamphiaster has approached the animal pole still more 

 closely than in Fig. 43. The external aster has thereby become more conspicuously 

 unsymmetrical. The spindle is more distinctly marked, and shows the equatorial 

 zone just dividing into its lateral halves. Both asters exhibit large areal corpus- 

 cles. The "halos" around each should be narrower ; more as in Fig. 43. 



Fig. 49. Living egg at the close of the formation of the first polar globule. Radi- 



