34 E. E. JUST. 



is greatly resistant to Echinarachnius sperm while the Echinarach- 

 nius egg is easily fertilized by Arbacia sperm. (2) Echinarach- 

 nius egg- water activates but does not agglutinate Arbacia 

 sperm. Arbacia egg-water agglutinates Echinarachnius sperm. 

 This is a hetero-agglutination by a substance in Arbacia egg- 

 water separate from Arbacia fertilizin because it may be removed 

 from the egg- water by dilution, by repeatedly washing the eggs 

 and by precipitating it with Echinarachnius sperm. It is found 

 in Arbacia blood. The microscopic appearance of this toxic 

 hetero-agglutination of Echinarachnius sperm is different from 

 that of the iso-agglutination. 



IV. DISCUSSION. 



Every egg has a fertilizable period during which falls its opti- 

 mum capacity for fertilization. Thus, Asterias eggs normally 

 shed after complete maturation are capable of fertilization on 

 immediate insemination but if procured by placing the ovaries 

 in sea-water these eggs, in the germinal vesicle stage, fertilize 

 only after the maturation process. Apparently, this is true of 

 Chcztopterus and Cerebratulus eggs which come into sea-water in 

 the germinal vesicle stage: insemination is most effective after 

 the germinal vesicle fades and the first maturation spindle is at 

 the mesophase. 1 Immature eggs will not fertilize though sperm 

 may bore into such eggs. Thus, in preparations of the normal 

 fertilization of Arbacia, I find many ovocytes with one or more 

 sperm in the cytoplasm, in some cases around the germinal 

 vesicles. Such sperm undergo no change. Moreover, sperm 

 may normally enter immature eggs according to Hempelmann, 

 Shearer and von Hofsten. Sperm entry, therefore, is no criterion 

 of fertilization. Moreover, the fertilizable period of an egg 

 gradually passes over as can be shown by the process of staling, 

 allowing the eggs to stand in normal sea-water. This may take 

 place as in Platynereis in an almost incredibly short time; in 

 Echinarachnius the time before capacity for fertilization is lost 

 is much longer though not so long as in Arbacia. Sperm may 



1 Wilson has found that in Cerebratulus after the germinal vesicle has broken 

 down, merogony is possible; enucleated fragments after insemination are not capable 

 of refertilization. (Cf. also Delage.) 



