294 ANIMAL SKETCHES. CHAP. 



pincer-jaws with much force, put your little finger in 

 between the nippers of a living crayfish. This will 

 probably satisfy you. But don't blame me if it hurts. 



I want you next to look at the carapace, as the shelly 

 armour, in front of what we have termed the tail, is 

 called. Looking at the back of the crayfish, we see that 

 it is a continuous unjointed sheet. But it is divided by a 

 well-marked curved groove into a front part and a hinder 

 part. And the hinder part is divided by shallower grooves 

 into a narrow middle portion and a broader portion 

 bending round on either side. Turning the crayfish over, 

 we find that these side pieces end off just above where 

 the legs join the body. We can lift up the edge (which 

 is fringed with hairs) and see a little way under it. But 

 we must now examine more openly what lies beneath it. 

 By inserting our scissors under the edge at the front end 

 of the well-marked groove, which we have noticed on the 

 carapace, and cutting along the groove till we meet the 

 shallower groove, and then following this to the hinder 

 edge of the carapace, we shall remove a large flap. We 

 shall not have cut into the inside of the body, but only 

 into a side chamber which contains the gills. We notice 

 that those which we see are attached to the base of the 

 legs, and when we move the legs we disturb the gill 

 attached to it. There are other gills attached to the 

 sides of the respiratory chamber. You should look at 

 them under water, and you will then see that they are 

 like delicate curved plumes. All the blood of the body 

 must pass through these gill-plumes on its way to the 

 heart. And over them a continuous current of fresh water 

 is drawn through the respiratory chamber by a long 

 flattened plate near its front end, which acts as a sort of 

 screw-paddle. By attentively watching a living crayfish, 

 you may see little specks of sediment in the water shot 



