These inner three pairs should also be detached, and the whole of the mouth organs arranged on a card thus:-- MANDIBLES. FIRST MAXILLAE. SECOND MAXILLAE. FIRST MAXILLIPEDES. SECOND MAXILLIPEDES. THIRD MAXILLIPEDES. The first attempt will certainly be unsuccessful; and the first few attempts will probably be unsatisfactory; but we shall gain knowledge with each successive trial. And knowledge is worth the winning. The stomach is interesting, and the gastric mill may be easily examined. When the mouth organs are removed, there will be no difficulty in taking out the stomach. This should be cut open with a needle, and then we shall see the gastric teeth (_g_ _g_) which grind up the food against the fixed calcareous plate (_b_ _b_). The lower end of the stomach is set with fine hairs, which prevent the passage of food into the intestines until it has been ground fine between these living millstones. A similar arrangement is found in all the higher Crustacea. The time spent in comparing the gastric mill of the Crab with the ‘gizzard’ of the Cockroach will not be thrown away. The Broad-clawed Porcelain Crab (_Porcella´na platyche´les_) is also worth keeping, for it is a droll little creature. These crabs are generally to be found clinging to the under surface of stones or of ledges of rocks overhanging small pools. The chief interest of these crabs, for us, lies in the exceedingly beautiful arrangement for procuring food with which the outer pair of foot-jaws is furnished. [Illustration: FIG. 70.--Stomach of Crab laid open. _b_ _b_ _b_, fixed plate, against which the gastric teeth _g_ _g_ are opposed; _b´_ _b´_, gastric teeth enlarged.]