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Handbook of Nature-Study 



THE CRAYFISH 



Teacher's Story 



HEN I look at a crayfish I envy it, so rich is it in 

 organs with which to do all that it has to do. 

 From the head to the tail, it is crowded with a 

 large assortment of executive appendages. In 

 this day of multiplicity of duties, if we poor 

 human creatures only had the crayfish's capa- 

 bilities, then might we hope to achieve what lies 

 before us. 



The most striking thing in the appearance of 

 the crayfish is the great pair of nippers on each of 

 the front legs. Wonderfully are its "thumb and 

 finger" put together; the "thumb" is jointed so 

 that it can move back and forth freely ; and both 

 are armed, along the inside edge, with saw.teeth and with a sharp claw at 

 the tip so that they can get a firm grip upon an object. Five segments in 

 these great legs can be easily seen; that joining the body is small, but 

 each successive one is wider and larger, to the great forceps at the end. 

 The two stout segments behind the nippers give strength, and also a 

 suppleness that enables the claws to be bent in any direction. 



The legs of the pair behind the big nippers have five segments readily 

 visible; but these legs are slender and the nippers at the end are small; 

 the third pair of legs is armed like the second pair; but the fourth and 

 fifth pairs lack the pincers, and end in a single claw. 



But the tale of the crayfish's legs is by no means told ; for between and 

 above the great pincers is a pair of short, small legs tipped with single 

 claws, and fringed on their inner edges. These are the ma.xillapeds, or 

 jaw-feet; and behind them, but too close to be seen easily, are two more 

 pairs of jaw-feet. As all of these jaw-feet assist at meals, the crayfish 

 apparently always has a "three fork" dinner; and as if to provide accom- 

 modations for so many eating utensils, it has three pairs of jaws all work- 

 ing sidewise, one behind the other. Two of these pairs are maxillae and 

 one, mandibles. The mandibles are the only ones we see as we look in 

 between the jaw-feet; they are notched along the biting edge. Con- 

 nected with the maxillae, on each side, are two pairs of threadlike flappers, 

 that wave back and forth vigorously and have to do with setting up cur- 

 rents of water over the gills. 



Thus we see that, in all, the crayfish has three pairs of jaw-feet, one 

 pair of great nippers and four pairs of walking feet, two of which also have 

 nippers and are used for digging and carrying. 



When we look upon the crayfish from above, we see that the head and 

 thorax are fastened solidly together, making what is called a cephalo- 

 thorax. The cephalothorax is covered with a shell called the carapace, 

 which is the name given also to the upper part of the turtle's shell. The 

 suture where the head joins the thorax is quite evident. In looking at 

 the head, the eyes first attract our attention; each is black and oval and 

 placed on the tip of a stalk, so it can be extended or retracted or pushed in 

 any direction, to look for danger. These eyes are like the compound eyes 

 of insects, in that they are made up of many small eyes, set together in a 

 honeycomb pattern. 



V. .s ., 



