374 



APPLIED BIOLOGY 



for land or terrestrial life, while most crustaceans have gills 

 for aquatic breathing. 



Lowest Crustaceans. Most fresh-water streams and ponds 

 contain numerous species of the smaller and lower Crustacea 

 known as copepods and water-fleas. These are very im- 

 portant in the food-supply of many fishes. As many forms 



FIG. 124. Dorsal 

 view of a copepod. 

 o, ocellus or eye- 

 spot ; a, antenna ; 

 r, reproductive or- 

 gans ; d, digestive 

 canal ; e, egg- 

 masses. (From 

 Brooks.) 



FIG. 125. A water-flea (Daphnia). ant. 1, 

 2, first and second antennae ; /, feet ; 

 ht, heart ; d.gl, digestive gland ; br.p, 

 brood-pouch in which embryos develop. 

 (After Glaus.) 



as possible should be collected with a fine-meshed net, and 

 examined with a hand-lens and low power of microscope. 

 Pictures in zoology books will help to identify those which 

 may be found in pond water. 



Barnacles. The most remarkably modified of lower crus- 

 taceans are the barnacles (Fig. 126) which are attached to 

 floating sea-weeds, timbers, and bottoms of ships, and the 

 closely-related rock-barnacles or acorn-shells which cover 

 rocks between high- and low-tide marks at the sea-shore. 

 The barnacles were formerly supposed to be long-necked 



