The data of the number of cell types of eukaryotes can be calculated. We know the number of cell types of adult human body is 210 [18] ; sponges have 12 kinds of cell types [19] ; the simplest multicellular organism Trichoplax adhaerens has 4 types of cell [20] ; C. elegans has 27 types of cell [21] . Because the tanscriptome size of specific cells are relatively fixed, it can be anticipated that the larger the size of complete transcriptome of an organism, the more the number of cell types. Based on the data of Valentine's [22] , a linear relationship between the number of cell types cn and the size of complete transcriptome x can be drawn (Fig 1) . The number of cell types can be roughly calculated as: