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-jertilization 
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, 
KGlliker 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 
