Artificial Parthenogenesis in Thalassema Mellita 105 



this point. Hunter ('04, p. 214) also records the presence of a 

 membrane surrounding unfertiHzed eggs of Arbacia after treat- 

 ment with MgClz- 



Loeb ('05), in a series of recent papers, has pubHshed the 

 results of experiments which have confirmed my observations 

 on the formation of a membrane after exposure of unfertilized 

 eggs to acid solutions. Although our observations agree as to 

 the power of acids to call forth a membrane formation, certain 

 marked differences occur in our results, and it may be well to 

 compare his experiments and my own in this place. By the use of 

 an improved method, Loeb has succeeded in closely imitating the 

 process of normal development in the unfertilized eggs of Strongy- 

 locentrotus purpuratus. If the eggs are treated with hypertonic 

 sea-water alone, no membrane is formed, and only a small per- 

 centage undergo any development at all. The rate of develop- 

 ment of these is much slower than in the case of fertilized eggs 

 and the larvae arising from them do not rise to the top but 

 swim ?.t the bottom of the dish. By first exposing the unfertilized 



eggs, however, to 50 cc. of sea-water to which 3 cc. — of a fatty 



acid, e. g., formic, acetic, propionic, butyric, valerianic or caproic 

 acid, are added, for from | to i^ minutes, they forma character- 

 istic fertilization membrane when put back into normal sea-water. 

 The membrane was not produced as long as the eggs were left in 

 the acidulated water, nor was it formed when they were taken out 

 a little too early or too late. Eggs treated with the acid alone do 

 not develop, but in a few hours begin to disintegrate, and ^fter 

 twenty-four hours practically all are dead. Subsequent treat- 

 ment, however, with hypertonic sea-water produces a surprising 

 result. If, after the appearance of the membrane, the eggs are 

 placed in 100 cc. of sea-water, to which 15 cc. of a 2| w NaCl 

 solution has been added, for from 20 to 50 minutes, 90 to 100 per 

 cent of the eggs develop with the normal rate of segmentation. 

 "A large percentage of the blastulae originating from this com- 

 bination of methods looked perfectly normal, and rose to the sur- 

 face of the sea-water. Their further development into gastrulae 

 and plutei occurred with the same velocity as that of the control 



