Most of the Polychaete worms possess integumentary processes which are labelled gills or branchiae in morphological text-books. These may occur segmentally along the whole length of the body, or they may be localised on a few segments in the middle region or at the anterior end of the body. Frequently they are nothing more than a simple unbranched projection of the integument, which, owing to the fact that it is vascular and performs no other obvious function, is termed a “gill.” Thus in Sedgwick’s Textbook of Zoology are found the following statements: In the Cirratulidae “on some of the segments the dorsal cirri are long and filamentous, and function as gills.” In the Spioniformia “the dorsal cirri may attain considerable size, and act as gills throughout the greater part of the body.” In Sabelliformia “the palps are large and vascular acting as respiratory and sensory organs.” In the Cambridge Natural...

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