Whales do not feed extensively while migrating. For the most part there is not time enough, nor is the food plentiful enough to make it worth the effort. However, in the polar seas the whale’s food is plentiful enough to discolor the water. On close examination, the discoloration proves to be caused by thousands of tiny shrimps which are very slender and less than one-half inch in length. These creatures congregate in swarms near the surface to feed on microscopic plants known as diatoms. The whales need only swim back and forth through these cloudlike aggregations to fill their mouths quickly with water and shrimp. With each mouthful, the water is expelled between the jaws through a mat of fibers which hangs down from the upper jaw. The shrimps, which are retained on the mat, fall down onto the tongue and are swallowed. The work of pushing out several tons of water with each feeding is done by the tremendous tongue. The fiber mats are the frayed inner side of enormous hornlike plates which grow down from the palate. The main body of each plate is placed edgewise to the outgoing water so that many plates are required to complete the mat which runs from the tip of the jaw to the corner of the mouth. These plates vary in size and stiffness from species to species. Some of the plates from the mouth of the bowhead whale are 12-14 feet in length, whereas in the finback whale the plates are 2-4 feet. There can be over 200 plates per side in the filtering structure. The frayed inner edge is constantly breaking off and the plates keep growing and fraying to provide the necessary thickness for the mat. Technically, these plates are called _baleen_. They were called whalebone by the whalers, and that is the name which is still used in commerce. The plates have no relationship to bones, nor could they be mistaken for them. The whalebone was assiduously collected and sold to be made into a variety of objects such as umbrella stays, corset stays, buggy whips and other articles which today are made of steel or plastic. There was a great demand for the product and a bowhead whale produced over a ton and one-half of whalebone valued back in the 17th century at over 400 English pounds, equivalent to about $10,000 today.