Behavior of the Germ-cells 181 



added and observed to stand vertically to the surface of the jelly 

 as they penetrated. If the piece of jelly was not first mixed 

 with the extract, the spermatozoa simply rotated on its surface. 

 On the other hand, starfish spermatozoa on coming into contact 

 with Arbacia jelly behave as with the simple jelly alone, i.e. 

 they do not stand vertically to it. The vertical position may be 

 due, von Dungern thinks, to the presence of some substance in 

 the extract that lowers the excitability of the spermatozoa to con- 

 tact. Much still remains obscure, but these results show clearly 

 some of the factors involved in fertilization and cross-fertiliza- 

 tion. 



Artificial Helps to Fertilization and to Cross- fertilization 



A number of embryologists have found that normal fertiliza- 

 tion may be assisted by adding certain substances to the water 

 in which the sperm are placed. These substances excite the 

 spermatozoa to greater activity, and in this or in other ways 

 promote fertilization. It has also been known for a long time 

 that the glands connected with the ducts of the male may secrete 

 substances that make the spermatozoa active. For instance, 

 Kolliker discovered that the secretion of the prostate glands of 

 the male greatly excites the spermatozoa. Ordinarily the sper- 

 matozoa are quiescent as long as they remain in the testes or 

 even in the ducts leading from them, but become active when the 

 secretions are added or when set free in water. Roux states that 

 the fertilization of the frog's egg is helped by the addition of one 

 fourth per cent sodium chloride to the water, and Wilson has 

 found that the spermatozoa of Patella can fertilize a much larger 

 proportion of the eggs if a little potassium hydroxide is added 

 to the sea water. Torelle and I have found that somewhat 

 immature sperm of the starfish can be made active by ether, am- 

 monia, salt solutions, etc., and will then fertilize the eggs. Von 

 Dungern had previously observed that extracts of the eggs of 

 the sea urchin excite immature spermatozoa to activity. 



The most striking case of this sort is that of the fertilization of 

 the sea-urchin egg by sperm of the starfish, recently described 



