A FIELD DAY AT ANNISQUAM. 151 



retreating tide twice in every twenty-four hours. To 

 obtaiii these forms we have recoiirse to the dredge, a net 

 with an iron rim, which scrapes the floor of the ocean and 

 brings up the treasures living there. 



On the surface of the water exists a fauna far different 

 from that found in the location already mentioned, and to 

 collect these a si rface net is employed. This is made of 

 thin cheese cloth and is dragged along the surface ; the 

 water readily passes through the tissne but the numberless 

 animals floating at the surface are retained in its meshes. 

 These surface forms are mostly minute, but at the same 

 time they are exceedingly interesting. Among the forms 

 will be found nunibers of larvse which delight the eye of 

 the einbrj'ologist, but the vast majority are minute crus- 

 taceans as yet all bat unknown to science. The myriads 

 of these surface swimmers are beyond all computation. 

 The product of an hour's collectiug with the surface net 

 can only be numbered by millions. 



