SURVEY OF INVERTEBRATES 



91 



There are the Cirripedes, or Barnacles, that early in their youth 

 settle down permanently to a sedentary existence, and thereby 

 foul the hulls of ships and encrust driftwood and stones on the 

 seashore. Then unrecognized by other than specialists are the 

 many kinds of microscopic Crustaceans, such as Daphnia, Cyclops, 

 and their allies. These so-called Water-fleas vie in numbers with 

 the Protozoa and microscopic plants in the vastness of open 

 seas as well as in many lakes. Thus they form a crucial part of 

 the food of larger animals, including Fishes, and so indirectly of 

 Man. (Figs. 51, 62-64.) 



Brain 



Antennule 



Antenna 



Digestive gland 



Shell gland 

 Heart 



Swimming feet 



Brood pouch 



Fig. 51. — Crustaceans. A, Edible Blue Crab, Callinedes; B, Fiddler 

 Crab, Gelasimus; C, Caprella; D, Daphnia, a Water-flea. (From Paulmier 

 and Claus.) 



Myriapoda. Passing to the Myriapoda we reach the terrestrial 

 Arthropods with long serpentine bodies, such as the more or less 

 flattened Centipedes and the rounded Millipedes, the latter with 

 the body segments united in pairs, so that there seem to be four 

 legs on each segment. But, as their names indicate, legs are plenti- 

 ful, in some Millipedes reaching well on toward two hundred. 

 Centipedes are carnivorous forms with poisonous jaws but Milli- 

 pedes are destructive vegetarians. (Fig. 52.) 



Insecta. Everyone knows various members of the Insecta, 

 familiarly represented by that most domestic of animals, the House 

 Fly, but probably few realize that the species of Insects outnumber 

 all the other species of the Animal Kingdom. (Figs. 53, 258.) 



