EGGS OF ASTERINA (PATIRIA) MINIATA. 



On this point I have no evidence. So it should be borne in mind 

 that the eggs used in these experiments, and presumably by Loeb, 

 who did a considerable amount of work upon artificial partheno- 

 genesis in this species, are not the normally shed eggs equivalent 

 to those which are fertilized in nature, but are probably prema- 

 turely shed eggs. It is very questionable, therefore, whether 

 parthenogenesis ever occurs in nature. It seems more probable 

 that the parthenogenetic eggs observed in these experiments re- 

 sult from the artificial conditions involved in shedding some of 

 the eggs prematurely. 



The eggs of Asterina are very hardy and resistant of the cyto- 

 lytic action of sea water. While the unmaturated oocytes of most 

 echinoderms begin to disintegrate within twenty-four hours, 

 those of Asterina frequently remain unchanged, as though in 

 stable equilibrium, for from four to eight days. I have before me 

 a number of microscopic whole mounts, showing numbers of 

 eggs and larvae of Asterina fixed in Bouin's solution on the eighth 

 day after fertilization, in which there occur a number of un- 

 matured oocytes with germinal vesicle clean-cut and spherical 

 and plasmosome well defined. This ability of the unripe eggs to 

 withstand disintegration is of great practical value in the study 

 of development, for the water is kept free from the products of 

 egg decay ; a decided advantage in view of the fact that where 

 there are small percentages of developing eggs surrounded by 

 large percentages of non-developing eggs, the former would have 

 very small chance of survival if the latter were to decay and foul 

 the water. 



EXPERIMENTAL DATA. 



Most of the detailed data on pathenogenesis in Asterina were 

 obtained during the month of May, 1920, although the phenom- 

 enon was noted incidentally throughout April. The month of 

 May seems to be the best month for work with Asterina as there 

 appear to be larger ovaries and more full-grown oocytes then 

 than earlier. Possibly June would be still better, though I have 

 not tried any experiments at that time. 



Some thirty-two experiments were made in all, and no two 

 gave exactly identical results. A large series of ten experiments 



