Phylum XVI 



Echinodermata, Class Asteroidea 



Order Forcipulata 



ASTERIAS FORBESI 



Henry J. Fry, Cornell University Medical College 



AT THE Marine Biological Laboratory Asterias eggs are in optimum 

 l condition from about the middle of May to late June or early 

 July. Thereafter they are obtainable sporadically until the middle of 

 September. 



Under natural conditions the eggs are shed at metaphase of the second 

 polar body cycle, a fact which the writer confirmed by the cytological 

 study of naturally shed eggs of three individuals. As Just (1928) has 

 noted, occasionally eggs are shed naturally in the laboratory, and then 

 usually when the moon is full. The usual method of obtaining eggs 

 under laboratory conditions is to remove the ovaries, and the eggs are 

 then shed in the germinal vesicle stage. Upon contact with the seawater 

 they develop as far as the stage at which they are shed naturally, i.e., 

 metaphase of the second polar body cycle; a fact which was also con- 

 firmed by the cytological study of the eggs of three individuals. They 

 stay in this stage unless they are fertilized. On the other hand, Pro- 

 fessor Chambers has informed the writer that he and others have found 

 that under laboratory conditions maturation goes to completion without 

 fertilization. 



Just's statement, "Asterias eggs are the most sensitive that I know," 

 ( 1928) voices the opinion of all who work with them. This sensitivity is 

 probably due to the abnormal conditions under which eggs are obtained 

 in the laboratory. Just's observations (1928) concerning methods of 

 handling them should be consulted by anyone unfamiliar with this ma- 

 terial. 



The males and females vary to an equal degree in size and color, and 

 they may not be distinguished externally. Only those with soft skins 

 and bulging arms have ripe gonads (Just, 1928). When obtaining 



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