MUSEUM OF COMPARATIVE ZOOLOGY. 621 



ate markings at the clear animal pole of the yolk. Numerous highly refractive 

 spermatozoa in the vicinity of the vitellus. 



Fig. 50. First archiamphiaster has migrated still farther than in Fig. 48 toward 

 the animal pole, the centre of the external aster having nearly attained the surface of 

 the yolk. The conical protuberance caused by ae is covered by a cap of finely granular 

 substance (compare text, p. 198). Lateral zones of spindle thickenings half-way 

 between the equator and the poles of the spindle. 



Fig. 51. A single ill-defined clear spot seen in the living egg, where the pronuclei 

 are found in the 'same egg hardened and cut (Figs. 52, 52*). Equatorial zone of clear 

 protoplasm, ipz. 



Figs. 52, 52*. The third and fourth of five sections through the egg, shown in 

 Fig. 51, the egg having been put in chromic acid immediately after the outlines 

 (Fig. 51) were made. Both pronuclei contain numerous nucleolar bodies joined by 

 irregular fibres, which thus produce an indistinct reticulum. 



In Fig. 52 are to be seen the two polar globules, nearly the whole of the female 

 pronucleus, a portion of the male pronucleus, and, near the border of the latter, an 

 incipient aster of J?, with a conspicuous highly refractive structure [aa') occupying 

 the centre of the astral area. 



In Fig. 52* is seen the remainder of the male pronucleus. No other aster had as 

 yet made its appearance in the yolk. 



PLATE III. 



Fig. 53. Archiamphiaster, whether the first or the second is uncertain. Con- 

 sult text at pp. 189, 206. 



Fig. 54. Another view of the same. The optical axis coincides with the axis of 

 the incipient spindle. The nuclear substance, largely accumulated on one side of 

 the spindle, is seen as though "projected" on the equatorial plane passing through 

 the centre of the internal (deeper) aster. 



Fig. 55. Second archiamphiaster. The spindle exceptionally slender. The yolk 

 about the animal pole is constricted by two or three rings, which give it a wavy out- 

 line when seen in optical section. Compare with the description of the formation of 

 polar globules in Clepsine, as given by Whitman ('78", pp. 232, 233, and separate, 

 pp. 18, 19, PL XIL Figs. 2-6). 



Fig. 56. Equatorial optical section of same. The external aster with spiral rays 

 projected ; optical axis slightly inclined from the spindle axis. 



Fig. 57. Internal aster of the second archiamphiaster, with compound curvature 

 of rays. Male and female pronuclei ; the centre of the aster nearer the latter. 

 "Interzonal filaments," exceptionally prominent, unite the second polar globule to 

 the vitellus. A thin pellicle (vitelline membrane ?) stretches over the second polar 

 globule, the first having become detached. Granulations of the yolk omitted. 



Fig. 58. Male and female pronuclei, the latter near, but not coinciding with, the 

 centre of the inner aster of the second archiamphiaster. In this figure only that por- 

 tion of the inner aster is shown which lies very near the surface of the yolk, the rays 

 of which are stout and nearly straight. The centre of the astral area is occupied by a 

 few granules not quite so conspicuous as the pronucleoli, and certainly not embraced 

 within the outline of the female pronucleus, which is well marked. Compare Fig. 78 

 or deeper portions of this aster. 



