359 
Medinia notata, female, 
x 
Fundulus heteroclitus, male. 
The reciprocal of the preceding cross was made four times. The per- 
centage of impregnation does not seem to run as high as in the reciprocal 
cross. Thus: 
Experiment 23b EAN A aeeeicae ats atl eA eLAC ell ts 
Fe Da Aan Rete ee ee tll pericent: 
Fy 130) Stearns ; ....88 per cent. 
ments 23b and 27 have no significance. The experiments show that under 
favorable conditions a very high per cent. of impregnation is possible—a 
condition probably varying but little from the normal. 
The condition of dispermy present to such a large extent in the recip- 
rocals does not obtain in this cross. 
The rate of development during the earlier stages was the same 
as that of the normal. ‘lhe process. however, showed a slowing during the 
later cleavage stages, as was shown by the normals pretty generally entering 
upon the germ-ring stage, earlier than the hybrids. Inspection of Table 2. 
in which the stages of the normals and hybrids are placed in parallet col- 
umns, will show that from this point the developmental processes were 
considerably slowed. Thus, when the blastopore is closed, and the eyes are 
present in the normals at + p. m. 6/15, the hybrids have reached only the 
stage where the embryo has crept 4 to % over the yolk. 
TABLE 2. 
MENIDIA NOTABA MENIDIA NOTATA 
TIME. x < 
MENIDIA NOTATA. FUNDULUS HETEROCLITUS. 
6.05 p. M., June 12. Fertilization. Fertilization. 
7.35 Pp. M., June 12. Begin. 2 cells. Begin. 2 cells. 
7.35 Pp. M., June 12. | Close of 2 cells. Close of 2 cells. 
8.50 Pp. M., June 12. Begin. 4 cells. Begin. 4 cells. 
9.15 Pp. m., June 12. Close of 4 cells. Close of 4 cells. 
9.26 p. M., June 12. Begin. 8 cells. Begin. 8 cells. 
10.08 p. m., June 12. Close 8 cells. Close 8 cells. 
10.20 Pp. M., June 12. Close 16 cells. Close 16 cells. 
10.35 p .m., June 12. Close 16 cells. Close 16 cells. 
11.05 Pp. M., June 12. Close 32 cells. Close 32 cells. 
5.55 A. M., June 13. Early cleavage. | Early cleavage. 
9.00 Pp. M., June 13. Germ ring. | Late cleavage and germ ring. 
9.00 a.m., June 14. | Germ ring to } over yolk. Early gastrula. 
1.30 ep. M., June 14. Begin. gastrula to close of blasto- | Early gastrula to 3 over yolk. 
pore. 
4.00 p. M., June 15. Blastopore closed and eyes present. 3 to 3 over yolk. 
2.00 p. M., June 17. Emb. incompletely formed, optic 
ves. showing. 
2.00 Pp. M., June 18. No further along. 
