PAR THENOGENESIS 



shallow dishes so that evaporation takes place, the eggs 

 develop when transferred to normal sea-water. Similarly, 

 sea-water to which solutions of sodium or potassium chloride 

 have been added induces development. Thus, hypertonic 

 sea-water is a means of calling forth parthenogenesis. 



Butyric acid in sea-water, like carbon-dioxide, also 

 induces parthenogenesis in the eggs of Asterias forbesii. 

 R. S. Lillie has studied the relation of the duration of the 

 treatment with this acid in sea-water to the degree of 

 response elicited. He obtained only membrane-separation 

 with short exposure; membrane-separation and cleavage 

 with a longer exposure, and full development to the swim- 

 ming stage by a still farther increased length of exposure. 

 Increased temperature of the sea-water alone or combined 

 with butyric acid, and two short exposures to the acid sepa- 

 rated by the residence of the eggs in normal sea-water are 

 also successful. Any one of these methods is superior to 

 the hypertonic sea-water method by giving higher percent- 

 age of parthenogenetic development. 



In 1876 Richard Greef reported that he had observed the 

 parthenogenetic development of the eggs of a starfish, 

 Asteracanthion [Asterias) to the ciliated larval stage (gas- 

 trula). The larvae obtained were vigorous and corre- 

 sponded thoroughly with those developed from fertilized 

 eggs. Since Greef had taken every precaution against the 

 accidental presence of spermatozoa, since further the ani- 

 mals from which the eggs came gave no evidence of being 

 hermaphroditic,^ and since, as he had learned before, ferti- 

 lized eggs reach first cleavage in one to two hours after 

 insemination, whilst these parthenogenetic ones cleaved 

 first only at ten to twelve hours after having come into sea- 

 water, he was certain that he had observed a true case of 



^ Hermaphroditism among star^sh is rare. See Retziiis, /(?//, 

 Vol. 16 of his collected zvorks; Buchner, ipil. 



2rj 



