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THE POPULAR SCIENCE MONTHLY 



called swimmerets or little swimmers. The lower joints of these 

 paddles have two broad, flat toes. The paddles on the last or sixth 

 somite are different from the others ; they are wider and turned 

 backward (Fig. 15) so as to lie at each side of the tail-piece, telson ; 

 and these great-fingered paddles, taken with the telson, form what 

 is called the tail-fin. The nnder or ventral part of each somite, which 

 lies between the paddles, is called the sternum. The rounded upper 

 or dorsal part of the body-piece is the tergnm, which means the 

 back. In front of the abdomen, with its somites, is the cephalo- 

 thorax. This cephalo-thorax has a tergum, or back part, a sternum, 

 or under part, a pleuron, or side part (Fig. 15), and so many things 



Side, or rieuron. 



Paddle, or Swimmeret. 



Flat Toes. 



C 3 

 - 3 



o 



c o 



Fig. 1C. One of Lobster's Body-pieces, or Somites. 



are hanging down from it one can hardly count, much less learn them. 

 Counting from behind forward, you will find between the lobster's 

 body, or abdomen, and the head, eight pair of jointed legs, one pair 

 much longer and larger than the others, with huge pincers at the 

 ends. All these eight pair are called the thoracic appendages, be- 

 cause they are fastened to the thorax, or breastplate. The lobster uses 

 the four back-pairs for walking, and so they are called the ambulatory 

 limbs. The last pair has seven joints, and every joint works in a dif- 

 ferent direction ; so, when these hind-legs start off, it is hard to tell 

 Avhere they intend to go. The next pair of w r alking-legs are like the 

 hindmost pair, except that the first joint sends out a piece above it, 

 which is kept out of sight in a little room in the side of the lobster 

 (Fig. 22). We shall say more about this room by-and-by. The 

 two front pair of walking-legs send up pieces also into this chamber, 

 but the end of the leg is different from the last two pairs, for they 



