THE FERTILISATION OF THE EGG i8i 



reinforce the teleological view that hemaphroditism, so widely 

 spread among parasitic and sedentary organisms, is an adapta- 

 tion to overcome the impediments to sexual intercourse in 

 these forms. In the Tunicate the eggs are much more readily 

 fertilised by sperm of another individual than by sperm 

 derived from the same individual. When a certain number 

 of eggs of an individual A of Ciona in a given volume of sea- 

 water are fertilised by the addition of a certain quantity B of 

 a sperm- suspension of another individual, the number of eggs 

 which segment is smaller than when an approximately 

 equivalent suspension A is fertilised by an equivalent amount 

 of B in the presence of an extract made from the ovary on the 

 one hand, or from grinding up the eggs either of the individual 

 from which the eggs were obtained, the individual from which 

 the sperm was obtained, or a third individual. In the same way 

 the eggs of Arbacia and Strongylocentrotus contain substances 

 which increase the fertilising power of the sperm of the same 

 species. One may say in conclusion that there are a large 

 number of data available which suggest that eggs secrete sub- 

 stances which influence the sperm ; that there are indications 

 that these substances are of the same general character as 

 *' antibodies " ; and that possibly the action of some such 

 substances may facilitate fertilisation by a sperm of the same 

 species, while other substances tend to prevent union with 

 sperm of another species. But the last proposition remains to 

 be proved. 



Further Reading 



LiLLiE. Problems of Fertilisation. Chicago University Press. 



LoEB. Artificial Parthenogenesis and Fertilisation. Ide7n. 



For later work consult : 



Carter (1924). On the Early Development of the Echinoderm Egg. 



Proc. Camb. Phil. Soc. (Biol.) i. 

 Shearer (1922). On the Oxidation Processes of the Echinoderm Egg 



during Fertilisation. Proc. Roy. Soc. B. 93. 



