365 
Fundulus heteroclitus, female, 
x 
Gasterosteus bispinosus, male. 
The percentage of eggs impregnated may be nearly normal, thus: 
Hixperimient, :26deesee esiese se wenn eee 86 per cent. 
a LOS GER ee aN ae eet eae LS s ste 
A very few of the eggs may be polyspermic. The details of the de- 
velopment of the hybrid and the normals occur in the table following. It 
will be noticed that the developmental processes keep apace until the close 
of cleavage. During the formation of the embryo the hybrids fall percep- 
tibly behind. Most of the eggs go to the closure of the blastopore, although 
this is accomplished in many eggs only imperfectly. The embryos are 
largely shorter than the normals. The details of development are item- 
ized in Table 5. 
TABLE 5. 
i. REG er Cee 2 Sg 
TIMe. | Funputus X Funputus. | FUNDULUS X GASTEROSTEUS. 
| 
2.40 p. M., June 30. | Fertilization. Fertilization. 
5.00 Pp. M., June 30. Well along in 2 cells. | Well along in 2 cells. 
5.12 p. m., June 30. Begin. 4 cells. Begin. 4 cells. 
5.57 Pp. M., June 30. Still in 4 cells. Begin. 8 cells. 
6.03 p. M., June 30. | Just begin. 8 cells. Mostly well along in 8 cells. 
6.05 p. M., June 30. _ Mostly well along in 8 cells. Well along in 8 cells. 
11.00 a.., July 1. | Toward close of segmentation. || Toward close of segmentation. 
12.30 rp. m. July 1., | Late segmentation. Late segmentation. 
1.30 Pp. m., July 1. Begin. gastrulation. Begin. gastrulation. 
9.00 p. M., July 1. | 4 over yolk. 1 over yolk. 
11,00 a. M., July 2. | 2 + over yolk. | Mostly } + over yolk. 
12.00 o., July 4. | Embryos formed, brain vesicles, | Embryos formed but no indica- 
| ete. | tion of brain vesicles, ete. 
12.00 m., July 7. | Eyes formed; tall. About same as in previous stage. 
Gasterosteus bispinosus, female, 
x 
Fundulus heteroclitus, mate. 
This cross was made three times, and in one case all the eggs were 
impregnated. There is the same high mortality usual during gastrulation 
in these hybrids. Those eggs that laid down the embryo showed the latter 
very much shortened and the head end very much thickened, many of the 
embryos appearing to be only head, Rudimentary eyes may form. Details 
