After the microscope is widely used, many single-celled organisms have the characteristics of both animals and plants (such as euglena, etc.). ). This intermediate type of organism is evidence of evolution, but it is a difficult problem to classify. After the publication of Darwin's Origin of Species in 1859, Hogg (J.Hogg, 1860) and Heickell (E.Haeckel, 1866) put all unicellular organisms and some simple multicellular animals and plants, including bacteria, algae, fungi and protozoa.