82 



CRABS AND INSECTS. 



antennae, that secrete a glutinous substance for the pur-- 

 pose. C, D, E show the successive stages to the adult 



form, in which the shell is mul- 

 tivalve, the animal anchored by 

 its head, and its feet modified 

 into cirri, that waft food into the 

 shell and mouth. Goose barna- 

 cles are connected with the bot- 

 tom or floating objects by long, 

 leathery pedicles. They have 

 no gills, breathing through their 

 skin. 



NOTE. Barnacles grow on whales, 

 turtles, and floating objects of all 

 kinds. Goose - barnacles have been 

 found six inches long growing in the 

 mouth of a large sun-fish (mola\ and 

 a barnacle is found on the feathers of 

 penguins in the South Atlantic. 



Order II. Water -Fleas 



(Entomostraca). A common ex- 

 ample is seen in the Cyclops, 

 found in fresh water, that may be distinguished by its sin- 

 gle eye and egg-sacs. It is just visible to the naked eye. 

 Most of this order are parasites upon fishes. The Ler- 

 naans (Fig. 90) live upon the gills of various fishes ; the 

 Caligus preys upon holibut, rays, etc., the Argulus upon 

 the alewife, the Penella upon the sword-fish and sun-fish, 

 while the Nogatus preys upon the man-eater shark. They 

 have no gills, breathing through the body-walls or skin. 



Order III. Leaf- footed Crustaceans (Branchiopo- 

 da). These animals breathe by broad, leaf-like gills upon 

 their feet, and secrete a bivalve shell. The Artemia* or 



* Artemia salina (Fig. 91, ft) has been made to acquire the charac- 

 teristics of Branchipus (Fig. 91, a} by gradually diluting the water 

 until it was fresh, 



FIG. 88. Upper part of adult 

 barnacle, showing appear- 

 ance of cirri under the mi- 

 croscope. 



