The Medusæ have no other means of breathing but through the skin. We remark all over the body of these zoophytes certain cutaneous elongations, disposed so as to favour the exercise of the breathing function. Certain marginal fringes of extended surface, as well as the tentacle, are the special seats of the apparatus. The organs of digestion also present arrangements peculiar to themselves; the mouth is placed on the lower part of the body, and is pierced at the extremity of a trumpet-like tube, hanging sometimes like the tongue of a bell. The walls of the stomach, again, are furnished with a multitude of appendages, which have their origin in the cavity of the organ, and which are very elastic. The stomach, furnished with these vibratile cells, appears to secrete a juice whose function is to decompose the food and render it digestible. [Illustration: Fig. 91. Cassiopea Andromeda (Tilesius).] In some of the Medusadæ the central mouth is absent altogether. With the Rhizostoma, for instance, the stomachal reservoir has no inferior orifice; it communicates laterally with the canals which descend through the thickness of the arms, and open at their extremities through a multitude of small mouths. These are the root-like openings from which the animals derive their name of Rhizostoma, from the Greek words ῥίζα, root, and στόμα, mouth. [Illustration: Fig. 92. Cephea Cyclophora.] The arms of the Rhizostoma are usually eight in number, the free extremities of each being slightly enlarged: in these arms many small openings or mouths occur, which are the entrances to so many ascending canals communicating with larger ones, as the veins do in the higher animals: the common trunk canal is thus formed, which directs itself to the stomach, receiving in its way thither all the lateral branches. A very distinct circulation exists in the Medusæ. The peripheric part of the stomach suffers the nourishing liquid which has been elaborated in the digestive cavity to pass: this fluid then circulates through numerous canals, the existence of which have been clearly traced.