HAEMOGLOBIN is found in the Crustacea. It occurs dissolved in the blood plasma of the Notostraca1,2, Anostraca3, Cladocera3,4, and parasitic Copepoda5,6 although it is absent in free-living ones2. I have not been able to find haemoglobin in the Branchiura (Argulus). It is found, however, in Ostracoda7 and in a parasitic member of the Cirripedia8. All these groups are Entomostraca ; haemoglobin is unknown in the Malacostraca. Among the latter, the Decapoda have haemocyanin as a respiratory blood pigment. I have now found haemoglobin in the one remaining group of the Entomostraca, namely, the Conchostraca, in which, to my knowledge, it has not yet been sought.