136 CRAYFiSH, LOBSTERS, SPIDERS, AND INSECTS 



while the opposite end is firmly attached to some sub- 

 merged object. The body of the barnacle is inclosed in a 

 sort of bivalved shell which, in reahty, is composed of five 

 distinct pieces so arranged _,^---.-,-.^w-<aiE=v:;--.— -;■.. 

 that they form two valves, . ^^^^^ ^ ^^^^ ^^^^^^^ 

 — hence the bivalved ap- 

 pearance, by which the barnacles re- 

 semble clamlike mollusks. 



The acorn barnacles have no stalk and 

 resemble low, blunt pyramids in form. 

 They are found attached to rocks and piles 

 between tide marks, to ship bottoms, and 

 some species, at least, are sometimes found 

 attached to the bodies of whales. Some 

 species of acorn barnacles grow eight or 

 nine inches in length and are sometimes 

 eaten for food. 



The life history of barnacles is rather 

 complex. The adult lays eggs that hatch 

 into queer Httle animals, each of which is 

 called a naupUus, which one would never 

 imagine to be connected with an adult 

 barnacle. After a time this changes into 

 another and different form called the cypris 

 form. Finally this, through successive 

 changes, develops into the adult barnacle. 

 Barnacles are pecuhar in having no heart and no distinct 

 blood vessels. 



Shrimps. — The shrimps are very closely related to the 

 lobsters and crayfish, and are also of considerable impor- 

 tance as an article of food. The common shrimp occius in 

 abundance on the eastern coast of North America, from 



Fig. 73. — Stalked 

 barnacle. 



