PROPERTIES OF PROTOPLASM 15 



involving sex differentiation, and are called sexual reproduction. 

 These consist, both in animals and plants, in the fertilization 

 of an egg derived from a female organism, by a spermatozoon 

 derived from a male, and after the union of egg and spermato- 

 zoon an embryo is produced which grows through many differ- 

 ent stages in development (ontogeny) to an adult organism 

 similar to the parent form. In some cases the egg proceeds to 

 develop without processes of fertilization, such a method of 



FIG. 6. Spore formation in a gregarine. From a photograph. 



reproduction being known as parthenogenesis, a result which 

 may be brought about in some cases, artificially, by the use of 

 salts. 



5. POWER or ADAPTATION 



A fifth property possessed by protoplasm is the capacity to 

 vary under changed conditions of the environment. It is by 

 reason of this power that the myriads of animal and plant forms 

 exist today as distinct species. Such variations, due perhaps 

 to environmental differences, perhaps to mutations or sudden 

 and unexplained appearance, are rarely observed in the making, 

 but the result of the change or changes is spoken of as an adapta- 

 tion. Such adaptations may be in structure or in function and 



