Relatively few data are available on blood circulation in pulmonates. For several reasons the study of circulation in these animals is difficult. First, the circulatory system is of the open type, but it is complex, i.e., a variety of mechanisms, especially concerning the transport of venous blood, is found within the animals. Second, it is generally assumed that the blood flow is regulated to a large extent by muscular movements both of organs and of the entire animal. For this reason it is difficult to assess patterns of blood flow direction. This means that in these animals the study of circulation must be related to behavioural aspects, and such a dynamic approach is not easy to realize. Third, an adequate study of circulation must also refer to respiration and in pulmonates different systems of respiration coexist: in the lung and the skin. The relative role of these respiratory systems depends on environ- mental conditions. Consequently, in the case ofpulmonates a functional understanding of circulation is only possible in ecological contexts. Fourth, the preservation of the circulatory structures is difficult, due to the fact that many parts of the body of pulmonates are soft and loosely structured, while the circulation is of the open type. Fifth, both interspecific and intraspecific differences frequently occur in the circulatory system of pulmonates.