Temperature and Heart Rate in Pterotrachea

The at tempt to give form and substance to various possibilities suggested by a study of thermal increments at present calls for an increase in the available data. I t is necessary to analyze a greater array of biological processes in a greater variety of forms. Since the fauna at Naples affords abundant opportunities for investigations of this character, a number of organisms fairly common there were explored and, for the purposes in mind, the heart rates of the large heteropod Pterotrachea coronata and of the pteropod Tiedemannia neapolitana proved to be, in several respects, almost ideal. Aside from the great convenience of being completely transparent, both animals are very sensitive and permeable to heat, and their hearts are large enough to be seen clearly without a lens, under practically all circumstances. At intermediate temperatures pulsation in Pterotrachea in unit time is approximately twice as fast as in Tiedemannia where ten beats require slightly over 0.4 of a minute between 14 ° and 15 ° . Moreover, there are significant differences and resemblances between these two forms,--a fact which has acquired additional interest since Crozier and Stier (1924-25, a), have reported one