To study the morphology and physiology of blood cells from five species of heterotherm vertebrates（carp Cyprinus carpio,crucian Carassius auratus,catfish Silurus asotus,toad Bufo bufo gar-garizans and Chinese soft-shelled turtle Pelodiscus sinensis）,three kinds of living cells（thrombocytes,small lymphocytes,erythrocytes）were obtained from the experimental animals.Plasma samples were partly anticoagulated with trisodium citrate,potassium oxalate and magnesium sulphate（MgSO4）at 23℃ in vitro,and observed in the light microscope and scanning electron microscope.Results showed that:1)small lymphocytes were typically spherical and normally dispersed in oxalate-plasma from all of the experiment animals and in citrated-plasma from carp and crucian.However,they were aggregated in MgSO4-plasma from all of the experiment animals and in citrated-plasma from catfish,toad and Chinese soft-shelled turtle.2)thrombocytes were dispersive and spindle or elliptical in shape in oxalate-plasma from the five species of experimental animals;in citrated-plasma from carp,crucian and catfish;in MgSO4-plasma from carp,crucian,catfish and Chinese soft-shelled turtle.However,they were aggregated in citrated-plasma from toad and Chinese soft-shelled turtle,and in the MgSO4-plasma from toad.3)erythrocytes were typically normal,and not haemolytic in citrated-plasma and in MgSO4-plasma from five species of experimental animals,but they were completely haemolytic in oxalate-plasma from experimental animals except for toads.Rouleaux formation of erythrocytes,such as occurs in mammalian plasma,was not observed in the experimental animals.We conclude that:1)the same of small lymphocytes or the thrombocytes in heterotherm vertebrate plasma possess the ability to aggregate together in vitro,the process of the aggregation may relate to plasma Ca 2+ and Mg 2+ concentration;2)the process of erythrocyte sedimentation caused by their specific gravity in plasma of these experimental animals,is different from that caused by rouleaux formation of
