The Heart.

The sinns venosus is a triangular chamber into which run the ductus Cuvieri of the right and left sides. It opens into the atrium, which, is a large, thin-walled chamber. This lies dorsal to the ventricle into which it opens on the left side. The ventricle has very thick muscular walls and is asymmetrical, being rather larger on the left side than on the right. It runs forward, narrowing into the conus arteriosus. The valves of the conus have been used to a certain extent in classification. In the most primitive sharks there are three longitudinal rows of four valves. In most sharks this number is decreased, while in rays it is increased, at least this is the general supposition. But of the animals examined, R. nasuta, the stingray and Torpedo, all resemble the primitive sharks in having three long rows each containing four valves. In Typhlonarke one of the rows