162 CONVERSATIONS ON 



these leaves or sticks floating towards the tail 

 of the grub, and afterward driven off again. 

 This is because the insect is pumping in 

 water, and then throwing it out. If you take 

 one of them out of the water, and hold it with 

 its head down, and let a drop of water fall 

 upon its tail, it instantly sucks it in, and you 

 can see it grow larger ; and when it throws it 

 out again it becomes smaller." 



"But, Uncle Philip, how can you see it 

 suck the water in ?" 



"Very easily, boys. When it is in the 

 water, if you will colour some other water 

 with indigo, or ink, or any thing else, and 

 then hold a glass tube just over the tail of 

 the insect, and very carefully put some of the 

 coloured water into the tube, you will soon see 

 the grub spirt out a stream of it to the dis- 

 tance of several inches : or if you will put the 

 insect in a saucer of coloured water, and then 

 suddenly move it, and put it into one of clean 

 water, you will see it spirt out the coloured 

 stream plainer still." 



" Why, Uncle Philip, it must have a pump 

 inside of it." 



"It has, boys, something very like one. 

 This stream of water is forced out to help 



