CARL R. MOORE. 



results obtained by the writer with the eggs of Arbacia do not 

 agree with the observations of Professor Loeb on the eggs of the 

 California sea-urchin. 



The eggs of Arbacia will, as does the above cited instance of 

 behavior of the Stronglyocentrotus egg, segment into two or 

 four cells and go no farther in development, but remain for 

 several hours apparently normal half or quarter eggs. This 

 condition is perhaps best obtained in Arbacia following a hyper- 

 tonic treatment of thirty to forty minutes, with the weaker 

 solution. If such a lot of eggs are returned to normal sea-water 

 and allowed to remain at room temperature (2i-23 C.) for 

 twenty-four hours, many of them will appear quite normal, 

 while all gradations of loss of pigment can be found. There 

 are present also many small eggs of half or quarter normal size 

 but the majority of these are not normal; most of them are 

 entirely or partially devoid of pigment; some few of them how- 

 ever do appear normal in color. If sperm are added to such 

 dishes and the effects of the insemination carefully noted, a few 

 very striking facts are to be observed: 



(i) The smaller eggs as well as the eggs that have not seg- 

 mented are surrounded by actively swimming spermatozoa but 

 they do not produce a fertilization membrane; 1 (2) many of 

 the unsegmented eggs will segment, but the blastomeres are not 

 held together. Since a good membrane is not produced, the 

 blastomeres may become entirely separated from each other 

 or be retained within the very thin jelly layer of the egg and not 

 be in contact with each other as they are normally. These 

 blastomeres may again divide giving rise, each, to two daughter 

 blastomeres that may again become separate, making four 

 individual blastomeres from the same egg or four quarter-eggs; 

 and these may go on dividing until a great mass of cells are 

 present but not held together. Some few of them (for instance 

 all those derived from one of the first two daughter cells) may 

 remain in loose approximation and perhaps give rise to a very 



1 In many cases eggs that have been exposed to the weaker concentration for a 

 short time only, will produce a quite typical membrane after insemination, but 

 those exposed for one hour to this solution, and allowed to remain standing for 

 twenty-four hours, are almost entirely devoid of any semblance of membrane 

 production after insemination. 



