MAY I make use of your columns to correct a statement in my article on Crustacea in vol. iv. of the “Cambridge Natural History.” which I am afraid may seriously mislead the reader? Referring to the alleged presence of haemoglobin in the blood of Branchipus and Daphnia, I have stated in a footnote on p. 30 that the fact that the red blood of Lernanthropus has been proved not to contain haemoglobin throws doubt on the reality of its presence in the other two animals. At the time of writing I was not aware that the authority on which the presence of haemoglobin in Branchipus and Daphnia rested, and I was inclined to impugn, was Sir Ray Lankester, who, in the late ‘sixties and early’ seventies, published a series of researches which laid the foundation of a comparative knowledge of the distribution of haemoglobin and similar respiratory pigments in the animal kingdom (see especially Proc. Roy. Soc., vol. xxi., December, 1872, p. 70). After reading these articles it is clear to me that Sir Ray Lankester's statement as to the presence of haemoglobin in the blood of Branchipus and Daphnia, resting as it does on careful microspectroscopic examination, is quite unaffected by what may or may not be the case in Lernanthropus, so that I can only withdraw my footnote with many apologies to him and to readers of the “Cambridge Natural History”. With regard to Lernanthropus and its allies, small Crustacea parasitic on fish and mussels, which possess a closed vascular system containing a red fluid, there is still some doubt. Van Beneden, who discovered Lernanthropus in 1880, states (Zoologischer Anzeiger, Bd. iii., p. 35) that he examined the blood spectroscopically, and found the oxyhaemoglobin lines.