SOME OF THE LIFE PROCESSES 127 



Vitamin E is one of the most recently discovered of the 

 vitamins. Its lack in food has serious effects on the repro- 

 ductive system. Animals deprived of it are either sterile 

 or unable to produce young strong enough to live. Lettuce, 

 cereals, meat, and egg yolks are the principal sources of this 

 vitamin. 



Methods of Reproduction. Every kind of animal has the 

 ability of producing individuals of the same species. Only 

 living things are capable of reproducing. Among animals 

 there are several different ways in which reproduction may 

 take place. Some of the simpler forms of life, which will be 

 discussed later, undergo a separation of the entire body 

 into two or more parts, each of which grows into a complete 

 animal. This simple and direct method of increasing num- 

 bers is called asexual reproduction. Most animals have a 

 much more complicated means of reproducing. In these, 

 special organs are set apart chiefly for the purpose of pro- 

 ducing young. These are the reproductive organs, such as 

 were described for the grasshopper. They consist of the 

 gonads, which produce the eggs and the sperm, besides 

 ducts and various other organs and structures used in the 

 reproductive process. Through sexual reproduction the 

 young is produced only after the egg and sperm have united 

 in the act of fertilization. The story of the creation of a 

 new individual from the fertilized egg is a long one. By 

 gradual and orderly changes, following a definite plan, the 

 simple, fertilized egg takes on the appearance of a living 

 creature. Some of these changes, which with others com- 

 prise the science of embryology, will be discussed in the 

 chapter on living matter and the cell (Chapter XIII). 



Glands of Internal Secretions. Within recent years much 

 has been learned about the glands which have no ducts but 

 empty their secretions directly into the blood. These are 

 called the endocrine glands or glands of internal secretion. 



