Embryonic respiration in the dogfish(Scyliorhinus caniculaL.)

Dogfish eggs would appear to be eminently suitable for physiological study because of their large size, easy availability (egg laying seems to be continuous throughout the year except for a break during the autumn (Craik, 1978)); their long lasting development (between 240 and 300 days from laying to hatching (Foulley & Mellinger, 1980a)); the clear separation between yolk-sac and embryo, and the fact that eggs are normally laid in pairs (opening up the possibility of keeping one of them as control whilst experimenting upon the other).