CHAPTER XIV 



REPRODUCTION 



REPRODUCTION is a process by means of which life is per- 

 petuated because the existence of individuals is limited. There 

 are two methods of reproduction the asexual and the sexual. 

 The former is the more primitive form, and is restricted to the 

 lower organisms. It is not difficult to conceive a reason for 

 reproduction in cells, for as the mass of living matter increases, 

 its volume increases as the cube, while its surface increases only 

 as the square. There will finally result, therefore, a condition 

 in which the absorptive surface is too small for the amount of 

 living matter, and a division will cause a relative increase of 

 surface. Sexual reproduction is derived probably from the 

 asexual method, and consists in the union of male and female 

 elements. The most primitive examples are to be found in 

 some of the unicellular organisms where there is a fusion of the 

 two sexes, known as conjugation. The resultant mass divides 

 and so produces its offspring. In somewhat more highly 

 differentiated forms there are simply an exchange and a fusion 

 of nuclear matter. In the higher animals there is a fusion of 

 nuclear matter of two individuals brought about by the pro- 

 duction of two kinds of sexual cells ova and spermatozoa. In 

 some animals, like the worms, both sexual elements exist in the 

 same individual, but this condition is found only abnormally 

 in the highest animals. Here the sexes present wide anatomical, 

 physiological, and psychological differences. These differences 

 fall into two groups primary and secondary. The primary 

 sexual characters are the most pronounced, and consist of those 

 pertaining to the sexual organs and their functions. The 

 secondary sexual characters are accessory to the primary ones, 

 and include the differences in voice, growth of hair on the face, 

 the mammary glands, etc., in man and woman. 



