Cut the stomach open. Note an anterior portion, the _cardiac chamber_, and a smaller posterior portion, the _pyloric chamber_. Examine its inner surface. What do you find here? This structure is called the _gastric mill_. Food, which for the most part consists of any dead organic matter, is chewed by the "stomach-teeth" into fine bits, and is then passed into the pyloric chamber. It is here that the digestive glands empty their secretion into the food. These glands have the same office as have the liver and pancreas combined in the toad, and so they are often called the _hepato-pancreas_. When the stomach has been removed there will be noted in the anterior portion of the body paired, flattened bodies, already mentioned, which connect with openings at the base of each of the antennæ by means of wide thin-walled sacs, the _ureters_. These organs are the _kidneys_, or _green glands_. Their office is similar to that of the kidneys in the toad, namely, the elimination of waste from the body. TECHNICAL NOTE.--Carefully remove all of the alimentary canal, digestive glands, and reproductive organs. This process will expose the floor of the cephalothorax. Now cut away from either side the horny floor or bridge at the bottom of the cephalothorax. If the specimen has not already been immersed, place it in clear water for further dissection. The foregoing dissection will expose the _central nervous system_. It extends as a series of paired _ganglia_ connected by a double nerve-cord along the ventral median line from the œsophagus to the last segment of the abdomen. From what points do the lateral nerves arise? Anteriorly the double nerve-cord divides, the two parts passing upward on each side of the œsophagus, where they again meet to form the _supra-œsophageal ganglion_ or _brain_. Where do the nerves run which rise from the brain? What is the difference between the position of the central nervous system in the crayfish and in the toad? Make a drawing of the nervous system.