Notes on a New Protozoon,Piridium sociabilen.gen., n.sp., from the Foot ofBuccinum undatum

The earliest stages found are groups of small bodies, 1·8 or 2·0μ in diameter. These groups are probably taken up by phagocytic cells and pass through the epithelium of the host into the connective tissue, where a cyst is formed by the host. Within the cyst the bodies grow. In many cysts there is a differentiation into two types: the larger, when mature, attain 40μ in size, are shaped like a pear, and contain at the broad end a chromatic rod. The small bodies reach 3Oμ in length, are also somewhat piriform, and contain two similar structures attached to their nuclei. In some cysts large bodies alone are found. Development is periodic, the youngest stages being found from January to March and the parasites not reaching maturity until September–November. Type speciesP. sociabile, with the features mentioned above: found near the ventral surface of the foot ofBuccinum undatum.