EGGS OF ASTERINA (PATIRIA) MINIATA. 113 



times more, will segment and develop into larvae. But the de- 

 velopment of these eggs is much slower than that of fertilized 

 eggs and, as a rule the larvae are not so perfect and die sooner." 

 "We have, therefore, two types of development in these (As- 



i 



terina) eggs. One type is represented by the fertilized egg, and 

 this type can be producecf artificially in a number of eggs, at least, 

 by calling forth the membrane formation by the above-named 

 artificial means. The second type is represented by the spon- 

 taneously developing egg in which no membrane has been called 

 forth; these latter eggs begin to segment later, and possibly 

 develop more slowly than the other eggs, and form larvae which 

 are not as perfect as those belonging to the first type." 



It will be seen that Loeb has touched upon some of the essential 

 points that are brought out in my experiments. He notes that 

 spontaneous parthenogenesis occurs in a small per cent, of eggs ; 

 that parthenogenetic cleavage takes place without membrane 

 formation ; that cleavage begins later ; and that development is 

 slower and less normal than is fertilized eggs. Loeb, however, 

 was not primarily interested in the course or results of spon- 

 taneous parthenogenesis, but merely dealt with it incidentally as a 

 check upon his work on artificial parthenogenesis or chemical 

 fertilization. He, therefore, merely points out the foregoing par- 

 ticulars without entering into any discussion as to their 

 significance. 



Spontaneous Membrane Formation. 



In only one important point is there lack of essential agreement 

 between his results and mine : he failed to note any cases of spon- 

 taneous membrane formation which was so frequently noted in 

 my experiments. I am at a loss to explain this discrepancy 

 between his results and mine, both performed at Pacific Grove 

 and both unquestionably safeguarded against accidental error. 

 Possibly the material behaves differently at different times of the 

 year and Loeb's work was done at quite a different time from 

 mine, which was confined to the last few days of April and the 

 first three weeks of May. The only difference in treatment be- 

 tween Loeb's cultures and mine had to do with the methods of 



