EGG-SECRETIONS OF ARBACIA AND ASTERIAS. 



369 



ARBACIA SPERM. 

 Experiment i. 



Experiment 2. 



Experiment 3. 



fertilization. One of the difficulties is the thigmotactic response 

 of the sperm, as this insures their sticking to surfaces they may 

 chance to meet. It is easy to see how under such circumstances 

 an accumulation about eggs might take place. While not 

 conclusive, experiments in which the surface of the eggs was very 

 materially reduced, and the jelly mass quite obliterated by 

 desiccation, showed that even in this case the sperm collect in 

 great numbers about the eggs. Minute fragments of egg- 

 powder are also centers about which the sperm aggregate in 

 great numbers. I have not observed this when powdered glass 

 or sand were added to the suspensions and as the surfaces in 

 these cases although of different physico-chemical properties, 

 must be assumed to be at least as extensive as in the egg-powder, 

 the marked sperm aggregation about the dried egg-fragments 

 and its absence about the other fragments is certainly in har- 

 mony with the idea that chemotaxis is a factor in bringing the 

 sperm to the egg. 



