PROPERTIES OF PROTOPLASM 



15 



esses involving sex differentiation, and are called sexual repro- 

 duction. These consist, both in animals and plants, in the fer- 

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

 spermatozoon derived from a male, and after the union of egg 

 and spermatozoon an embryo is produced which grows through 

 many different stages in development (ontogeny) to an adult 

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



FIG. 6. Asexual speculation in malaria organisms. A, parasite of tertian 

 malaria (Plasmodium vivax) in human blood corpuscle; B, multiple division 

 (schizogony) of same; C, multiple division of the organism causing quartan 

 malaria (Plasmodium malaria); c, blood corpuscles; m, melanin granules 

 formed by the parasites and liberated into the blood as a toxin during sporula- 

 tion; n, nuclei of parasite and progeny (merozoites) ; p, cell-body of parasite; v, 

 vacuole. From preparations. 



proceeds to develop without processes of fertilization, such a 

 method of reproduction being known as parthenogenesis, a 

 result which may be brought about in some cases, artificially, by 

 the use of salts. 



5. POWER OF 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 



