INTRODUCTORY 



THE object with which these Lectures were given was to 

 convey in as simple terms as possible the leading facts 

 relating to Sex in Animals and Plants, together with 

 suggestions bearing on the use and effect of sexual 

 propagation. Sex is a very wide-spread fact among 

 living things. Its manifestations are most obvious in 

 the Higher Animals and in the Higher Plants. But 

 sex is not general for all living organisms. Some very 

 simple and, as we believe, primitive beings are sexless, 

 while others show rudimentary sexual characters, others 

 again more advanced conditions. It is possible to arrange 

 such examples in order, so as to show how the sexual 

 mode of propagation may have come into existence, and 

 how in the rising scale of Animals and Plants the differ- 

 ence of the sexes became gradually more marked. This 

 is the evolutionary aspect of the theme, and it will be 

 taken up in the two first Lectures as it is seen in Plants. 

 The third and fourth Lectures will deal with the same 

 question in Animals. A discussion follows in the fifth 

 and sixth Lectures on Heredity. 



The whole body of any one of the higher Animals or 

 Plants is made up of various tissues, differing in texture 

 and in function. In the Animal body everyone recognizes 

 skin, muscle, bone, and nerve. In the Plant body 

 there is also an external skin ; tissues that are soft and 

 sappy when young lie within it, together with firmer 



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