The blood of the Invertebrata, like that of the Vertebrata, is not homogeneous. It consists of a transparent or semitransparent liquid, and a number of small, solid corpuscles which float in it.In the higher animals the corpuscles are of two kinds—red and colourless; but in the Invertebrata there are, as a rule, only colourless corpuscles. The red blood of Annelids is different from the red blood of Vertebrates, inasmuch as the plasma is coloured, and the corpuscles are colourless in the former, while in the latter the plasma is colourless, and there are present coloured and colourless corpuscles.