THE EFFECT OF SALINITY UPON THE RATE OF EXCYSTMENT OF ARTEMIA

¹ The Department of Biology, Stanford University

1. The excystment of Artemia takes place in two principal stages: first, the quiescent nauplius emerges from the shell of the cyst within a membranous sac, and then later the nauplius hatches from the sac and swims actively about.

2. The excystment of Artemia obtained from the margin of San Francisco Bay has been studied at 25° C. in diluted and concentrated sea water over a salinity range from zero (distilled water) to 225 per cent sea water (i.e., a solution in which the salt concentration is 225 per cent of the salt concentration of sea water. No salts precipitated out).

3. The same percentage of embryos emerged from the shells in all of these salinities, including zero salinity (distilled water).

4. In distilled water the emerged embryos are motionless and they do not hatch from the sac. Some swell and burst.

5. In 12 per cent sea water, 83 per cent of the emerged embryos hatch; in 25 per cent sea water 93 per cent hatch. In 50-225 per cent sea water 96-99 per cent hatch.

6. In 12-225 per cent sea water the nauplii that hatch are normal, active, and viable. They moult to form metanauplii before dying of starvation (in the absence of food) on about the fourth day.

7. In the salinity range 25-125 per cent sea water, the rates of emergence and hatching are practically constant (and therefore independent of change in osmotic pressure).

8. In the salinity range 150-225 per cent sea water the rates of emerging and hatching decrease with increasing salinity, but the interval between emergence and hatching is nearly constant throughout the range 25-225 per cent sea water.

9. Emergence is accelerated in 12 and 0 per cent sea water, but hatching is retarded in 12 per cent sea water and is inhibited in distilled water.