359 



Medinia notata, female, 



X 

 Fundulns heterocUtus, 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 14 per cent. 



" 27 : Small per cent. 



1.30 88 per cent. 



It is probable that the lower percentages of impregnation in experi- 

 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. The 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 parallel col- 

 umns, will show that from this point the developmental processes were 

 considerably slowed. '1 bus, when the blastopore is closed, and the eyes are 

 present in the normals at 4 p. m. 0/15. the hybrids have reached only the 

 stage where the embryo has crept h to 5 over the yolk. 



Table 2. 





Meniria 



notaba 



Menidia notata 



Time. 



X 





X 





Menidia 



NOTATA. 



Fundtjlus heteroclitus. 



6.05 p. M., June 12. 



Fertilization. 





Fertilization. 



7.35 r. M., June 12. 



Begin. 2 cells. 





Begin. 2 cells. 



7.35 P. M., June 12. 



Close of 2 cells. 





Close of 2 cells. 



8.50 p. M., June 12. 



Begin. 4 cells. 





Begin. 4 cells 



9.15 P. 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 p. M., June 12, 



Close 16 cells. 





Close 16 cells. 



10.35 p .M., June 12. 



Close 16 cells. 





Close 16 cells. 



11.05 p. M., June 12. 



Close 32 cells. 





Close 32 cells. 



5.55 A. M., June 13. 



Early cleavage. 





Early cleavage. 



9.00 p. M., June 13. 



Germ ring. 





Late cleavage and germ ring. 



9.00 A. M., June 14. 



Germ ring to i over 



yolk. 



Early gastrula. 



1.30 p. M,, June 14. 



Begin, gastrula to close of blasto- 



Early gastrula to j over yolk. 





pore. 







4.00 p. M., June 15. 



Bla.stopore closed and eyes present. 



§ to 5 over yolk. 



2.00 p. M., June 17. 







Emb. incompletely formed, optic 

 ves. showing. 



2.00 p. M., June 18. 







No further along. 



