Previous studies on the morphology of the lymphomyeloid tissues in the dogfish, Scyliorhinus canicula, have been confined to adults. This study was restricted to the structure and functioning of the developing immune system in embryonic and post-hatch dogfish. A major feature of the developing immune system in S. canicula, is the succession of haemopoietic/lymphoid tissues. The liver is the first tissue to contain immunoglobulin positive cells at 2 months, followed by the interstitial kidney at 3 months. The thymus, spleen, and Leydig organ appears at 4 months while the epigonal and gut-associated lymphomyeloid tissues are the last tissues to differentiate. The haemopoietic/lymphoid nature of the kidney and thymus disappear at post-hatch and the other lymphomyeloid tissues persist through adult life. By the time of egg case splitting (ca. 6 months), when embryos receive massive exposure to water-borne antigens, the structural development of most of the lymphomyeloid tissues is well advanced.