Miller's Thumbs. 317 



project, and they are kept clear of mud or sand so as 

 to answer the purpose of a doorway. I have watched 

 these operations many times, but never saw the 

 minnie attempt to enter the nest ; indeed, he could 

 not have done so, the opening not being large 

 enough. 



When the nest has reached the stage of comple- 

 tion it is easy to discover, because the, stickleback 

 keeps watch before it, and at that season his . breast 

 is of a bright crimson hue. He guards the nest with 

 the greatest care, and if he is tempted away for a 

 minute by some morsel of food he is back again 

 immediately. If a tiny twig or fibre comes along and 

 threatens to catch against the nest, he removes it in 

 his mouth, carrying it out into the stream that it may 

 be swept away. He also removes the sand when- 

 ever it begins to accumulate over much. It would 

 seem as if a current of fresh water were essential to 

 the ova, and that that is why the opening of the nest 

 is so carefully kept from becoming choked up. After 

 a while the fry come forth the most minute creatures 

 imaginable, mere lines about half the length of the 

 finger-nail. They play round the opening, and will 

 retreat within if alarmed. 



Where the brook passes under a bridge of some 

 size the current divides to go through several small 

 arches. There is here some fall, and the stream is 

 swift and bright, chafing round and bubbling over 

 stones. Here the ' miller's thumbs ' are numerous 

 a bottom fish growing to about four inches in length, 

 and with a head enormously broad and large in pro- 

 portion to its body. They rarely rise from the mud 

 or sand ; they hide behind stones, their heads buried 



