68 AN INTRODUCTION TO ZOOLOGY. 



in the higher animals this structure is not retained : 

 one kind of organ only, either male or female, is de- 

 veloped in one individual. In this case, the individuals 

 become dififerent in appearance, and the male develops 

 some distinctive character, as in the familiar case of 

 the cock, with its fine plumage, or the lion, with its 

 long mane. They also become different in character, 

 the female, devoted to the care of her offspring, being 

 gentle and peaceable, while the male, who has usually 

 to win his mate by fighting the other males, is com- 

 bative and fierce. This is the general rule ; but there 

 are some curious exceptions, in which, owing to some 

 unusual mode of life on the part of the species, the 

 female is stronger, or fiercer, or larger, than the male. 

 It may as a rule be stated, that the male animals of 

 any class differ more from those of allied species than 

 the females do from the females of allied species ; in 

 other words, the female usually shows us the normal, 

 or usual, the male an aberrant or unusual type. Next 

 to continuing its own life by eating, the most im- 

 portant function of any animal is to continue the race; 

 the sexual organs are therefore all-important parts 

 of the animal structure, and classification is very 

 largely based on their resemblances or variations. 



As has been already mentioned, some of the uni- 

 cellular organisms are able to reproduce themselves 

 by division, without any sexual process. The lower 

 forms of animal life nearly all do the same, while 

 they also reproduce themselves sexually. The asexual 

 reproduction is called " budding," because the new 



