The anatomical system of the starfish is easily traced by cutting off, with scissors, the skin from the dorsal surface of the disk, and also cutting a slit down one of the arms. In the center of the body will be seen the upper part of the stomach, a small star-like spot, from which radiate five branches, which divide and lead into the much-ramified, plume-like organs which extend through the arms. These are the pyloric cæca, whose function is to secrete the digestive fluids. The much-folded stomach occupies the greater part of the central space, its large convolutions showing on top. The mouth connects with the stomach on the ventral side. By turning back the skin from the arm, small filiform processes can in some large species be seen; these are the dermal branchiæ, or breathing-organs, which may either project through pores in the skin between the ossicles or be entirely retracted. If the pyloric cæca be laid back, one can see the rib-like arrangement of the ambulacral ossicles, and also the ampullæ, which lie between the ossicles on each side of the ridge. If an ampulla be inflated and then pressed, the corresponding tube-foot will be seen to extend. To follow successfully the water-vascular system, beginning in the madreporic plate and extending through the stone-canal to the ring-canal around the mouth and thence through the arms, requires a strong glass and more skilful manipulation. ORDER =PHANEROZONIA= FAMILY ~PORCELLANASTERIDÆ~ GENUS ^Ctenodiscus^ (Plate LII.) ^C. corniculatus.^ Pentagonal; about two and a half inches in diameter; the body flat, with wide marginal plates, giving a flat edge to the rather long, pointed arms; madreporic plate large; color greenish; ambulacra without suckers, seeming to be adapted to pushing through soft mud rather than dragging over hard surfaces. It lives in deep water on muddy bottoms and ranges from Massachusetts to Greenland. When dredged the animal is usually found to be filled with soft mud. FAMILY ~ASTROPECTINIDÆ~ In this family there are only two rows of tube-feet; the rays end in sharp points and have large ossicles on the margins. [pg209] GENUS ^Astropecten^ ^A. articularis.^ The body is flat and smooth; the rays sharply pointed and conspicuously bordered with marginal ossicles and fringed with short spines; two rows of ambulacral feet; color rich purple. Found in shallow waters of South Atlantic coast on sandy bottoms. (Plate LII.) GENUS ^Psilaster^ ^P. floræ.^ Diameter four to five inches; arms sharply pointed and conspicuously bordered with large ossicles; body flat, with smooth surface, the ossicles seeming like mosaic; bright pinkish flesh-color. It occurs in deep water off the eastern coast as far south as New Jersey. GENUS ^Luidia^ This genus of starfishes is celebrated for its peculiar habit of breaking in pieces when taken from the water, and therefore good specimens are almost impossible to obtain.