THE FERTILIZABLE PERIOD OF THE EGGS OF FUNDULUS HETEROCLITUS AND SOME ASSOCIATED PHENOMENA

¹ From the Marine Biological Laboratory, Woods Hole, Mass.

1. Sea water initiates development in the unfertilized eggs of Fundulus heteroclitus through the blastodisc stage, including the disappearance of platelets and formation of the perivitelline space. The blastodiscs of such eggs do not cleave. Eggs vary considerably in the rate and susceptibility to activation by sea water.

2. Fresh water and distilled water do not initiate development as efficiently as does sea water.

3. The fertilizable period of the average Fundulus egg in sea water is from 15 to 20 minutes.

4. A description of the passage of sperm through the micropyle system is given.

5. The perivitelline space appears to be formed principally by a change in the permeability of the egg cortex. As the yolk shrinks, it leaves the vitelline membrane to retain the original shape and size of the egg.

6. Evidence is adduced to show that the platelets are directly concerned in the formation of the blastodisc.

7. Although the early stages of development may be initiated in unfertilized eggs by the action of sea water, these stages are not independent in the fertilized eggs. They occur sooner and are of shorter duration in fertilized eggs. Furthermore, the percentage of eggs which develop these stages is higher in the fertilized than in the unfertilized eggs.

8. Insemination which is delayed for twenty or more minutes not only reduces the percentage of fertilization but also increases the percentage of abnormalities and decreases the percentage of hatched eggs in those lots which are fertilized.