Most of the recent contributions to our knowledge of the anatomy of gastropods have been in the field of “functional morphology,” concentrating especially upon the pallial cavity, and the digestive and reproductive systems. Here a valuable picture has been built up of the relation of structure to function. The more favoured systems of the classical morphologists—the vascular and nervous—do not, however, lend themselves so easily to functional treatment, and have come to receive much less emphasis. Though the older accounts of these systems—often in minute detail—fill many pages in Bronn's Tierreichs and other textbooks, there have of recent years been few good accounts of a prosobranch nervous or blood system. One of the most well known is that of Crofts (1929) on Haliotis.

Yet in soft-bodied animals like the Mollusca, in which the form of the body may be constantly changing, the distribution of blood in the haemocoele plays an important role in movements, and in changes of size and shape of the various organs. Especially in sedentary or slow-moving gastropods, which do not perform rapid muscular movements, we may think of the blood in the haemocoelic spaces as forming a “fluid skeleton”, and the pattern of the vascular system and the blood lacunae may have an adaptive importance entirely apart from the normal physiological role of the blood. It is therefore necessary to consider the “haemo-dynamics”, or the role played by the movements of large volumes of blood, for a full understanding of the mode of functioning of the various parts of the animal.

In the same way, the trend of recent discussions on the nervous system has moved away from the classical studies of the relative positions and degree of concentration of the ganglia. As Fretter and Graham have pointed out (1949) there can be euthyneurous “streptoneura” and streptoneurous “euthyneura”; and it is in general realised that concentration of the nervous system must have taken place many times by parallel evolution in different groups. The usefulness of the nervous system as a character in major taxonomy is thus likely to be much more limited than was once thought. Functional studies on the nervous system are of course best advanced in the cephalopods, following upon the work of Young; but already studies of nervous control of muscular systems in gastropods,

especially in relation to the buccal mass and feeding movements. (Nisbet, 1950) are giving to the nervous system in this group a new source of interest.

In the present paper it is proposed to continue the writer's recent accounts of the anatomy of Struthiolaria (reproductive system (1950), digestive system and pallial organs (1951)), and it is intended that this description of the vascular and nervous systems shall be read in the light of the previous work. For this reason, reference is made without detailed explanation to many of the structural and functional features that have already been described.