178 Experimental Zoology 
experiment, described above, in which he used a non-nucleated 
piece of the sea urchin’s egg and the spermatozoa of the crinoid 
produced larve entirely of the maternal type, which is the con- 
verse of Boveri’s result. 
Factors involved in the Entrance of the Spermatozoon 
The entrance of a foreign spermatozo6n into an egg is closely 
connected with the question of normal fertilization. What brings 
the sperm and egg together? How does the sperm enter the 
normal egg, and what delays or prevents its entrance into eggs of 
another specics? The immense collections of sperm around the 
egg in normal fertilization has led to the idea that the egg at- 
tracts the sperm. Certain experiments seemed to support this 
view. Pfeffer’s experiments with the antherozoids of ferns have 
often been cited as an instance of such an attraction. He found 
that when a dilute solution of malic acid was inclosed in open 
capillary tubes, and these tubes were immersed in a drop of 
water containing antherozoids, the latter collected around the 
open ends of the tubes, as though attracted by the malic acid. 
The evidence in favor of this interpretation has recently been 
considerably weakened by Jenning’s study of the behavior of 
protozoa. These also will collect in a drop of acid, not, how- 
ever, because they are attracted to the drop, but because no re- 
action takes place when they pass from water into a more acid 
solution. A reaction does occur, however, in passing from an 
acid region into water. The reaction involves a backing of the 
individual into the drop followed by a movement forward again 
in a new direction. On coming a second time to the edge of the 
acid area the reaction is again repeated. All individuals that 
pass by chance into the acid remain there — caught like rats in 
a trap —so that in time an accumulation occurs that might read- 
ily suggest that the animals had been attracted to this region. 
Strasburger claimed that the eggs of the seaweed, Fucus, 
excrete a substance that attracts the spermatozoén from a dis- 
tance of two diameters of the egg, but Bordet and Buller have 
failed to corroborate this observation. 
