lyS Experimejital 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 larvae entirely of the maternal type, which is the con- 

 verse of Boveri's result. 



Factors involved in the Entrance oj the Spermatozoon 



The entrance of a foreign spermatozoon 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 species ? The immense collections of sperm around the 

 egg in normal fertihzation 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 mahc 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 spermatozoon from a dis- 

 tance of two diameters jof the egg, but Bordet and Buller have 

 failed to corroborate this observation. 



