THE BIOLOGY OF THE CELL SURFACE 



tion are brought about. Prolonged exposure to weak or 

 short exposure to stronger hypertonic sea-water gives the 

 same results. With still longer exposure to hypertonic sea- 

 water, differentiation without cleavage is called forth. By 

 treatment with hypertonic sea-water I have never been 

 able to induce development with cytoplasmic cleavage in 

 this egg. Hypotonic sea-water also gives differentiation 

 without cleavage.^ I find that the percentage of swimming 

 forms may be increased by the addition of an acid or an 

 alkali to the dilute sea-water. Hypotonic sea-water in my 

 experience is an inferior means of inducing parthenogenesis 

 in this egg. Ultra-violet radiation also induces a qualita- 

 tively poor development.^ If eggs from a female from 

 whose body the sea-water has been removed, are placed on 

 a dry glass plate for a few moments, and are then put in 

 normal sea-water, a small percentage develops.'^ Eggs 

 having been kept at a temperature around 5°C. extrude 

 jelly at once when removed directly to normal sea-water at 

 room temperature (around 20°C.). Of these some will 

 develop farther. The best method for inducing the devel- 

 opment to the stage of larval worms, which can scarcely 

 be distinguished from those developed from normal, fer- 

 tilized eggs, is to expose eggs to sea-water at a temperature 

 of from 30 to 33°C.'* In this method it is necessary that 

 the eggs come directly from the female into the warm 

 sea-water without having lain in sea-water at room tempera- 

 ture. If eggs are taken from sea-water at room tempera- 

 ture, they need an exposure to a higher temperature, around 

 40°C., for about a minute to be stimulated to develop.'' In 



^ Just, ig2Se. 

 -Just, 1933c. 

 3 Just, 1915a. 

 ^ * Ibid. 



" Just^ unpi(bluhed observations. 

 ~ • 21S 



