82 CRABS AND INSECTS. 
antenne, that secrete a glutinous substance for the pur- 
pose. C, D, £ 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 gilis, 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 (#o/a), and 
a barnacle is found on the feathers of 
penguins in the South Atlantic. 
Fic. 88.—Upper part of adult 
barnacle, showing appear- Order II. Water- Fleas 
ance of cirri under the mi-  ( Fntomostraca).—A common ex- 
erie 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 Argudus upon 
the alewife, the Pene/la upon the sword-fish and sun-fish, 
while the Vogatus 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, 4) has been made to acquire the charac- 
teristics of Branchipus (Fig. 91, 2) by gradually diluting the water 
until it was fresh. 
