164 



SECRETS OF EARTH AND SEA 



can crawl like a leech and also swim freely by aid of their 

 wheel-apparatus ; (2) the naked free swimmers, which do 

 not crawl, but move only by swimming; (3) the turtle- 

 shelled free swimmers (Fig. 37) like the last, but provided 

 with strong, often faceted, angular, and spike-bearing 

 shells or " bucklers," from which head and wheel-apparatus 

 project in front and narrow tail behind ; (4) the rooted or 

 fixed forms (Figs. 37 bis) ; these never swim when full 

 grown, but each forms and inhabits a protective tube or 

 case ; (5) the skipping or darting forms. Of these there 

 is only the Pedalion mirum (Figs. 35 and 36), which is 

 quite unlike all the other wheel animalcules in having limbs 

 like those of the'jminute water-fleas (Nauplius, Cyclops) 

 which strike the water and are fringed with feather-like 

 hairs. 



The larval or young form of Crustacea known as " the Nauplius.'' This is 

 the ' ' Nauplius " of a kind of Prawn. The three pairs of branched limbs 

 are well seen. Much magnified. 



