The blood-vessel pulsations of the polychaete worm Perinereis cultrifera are adapted to environmental temperatures in that the rate for animals living in English waters is the same at 14d̀ as that for Mediterranean animals at 20d̀. At a given temperature the rate for the northern form is quicker than that for the southern form, in spite of the fact that the northern animals are considerably bigger.
The rates of heart-beat of Crustacea show a similar adaptation to latitude in five out of six pairs of comparable animals living respectively in seas round the British Isles and in the Mediterranean. In spite of the fact that in most cases the northern animals are bigger, they usually have a faster heart-rate at a given temperature than the southern forms.
The rates of scaphognathite movement of comparable prawns living at Plymouth and at Tamaris have also been measured. For species of Lennder there is a parallelism between scaphognathite and heart-rates, for Spinrontocaris and Hippolytethis is not the case.
The question is discussed as to whether physiological adaptation to latitude, when it exists within a single species, is genetical or individually acquired.
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