SEX DETERMINATION 237 



systems were probably first evolved in the gamophase, and during 

 evolution their action gets gradually pushed back in ontogeny. This 

 must entail the addition of factors which act earlier, but not necessarily 

 the loss of the factors which act at the later stages. The morphological 

 sex-differentiation evolved in this way may lose its primary function, as 

 it does in hermaphrodites with well-diiferentiated sex organs. 



In fact, if we regard sex from a morphological point of view, it 

 becomes an extremely ill-defined and imprecise concept. The impor- 

 tant difference between reproduction with or without crossing-over 

 becomes irrelevant, while there seems, from this point of view, to be 

 a fundamental distinction between fully developed sexuality such as 

 we see it in a strip-tease artist and mere self-sterility and incompati- 

 bility mechanisms. But this is a distinction which is very difficult to 

 define; on which side of the line shall we place the multipolar sexuality 

 of Fungi or the relative sexuality of Ectocarpus} 



