PHYLUM ARTHROPODA 



577 



permanently attached like the degenerate forms jnst described, but crawling 

 freely over the surface of the host. The body consists of an oval flattened 

 eephalo-thorax, and a small bilobed abdomen (ab.). The mandibles and maxilhc 

 are piercing organs enclosed in a sucking-tube or proboscis (r.), in front of which 

 is a median tube ending in a spine (sf.). The second maxilUe are divided into 

 two portions, the anterior of which {If.l) are modified into sucking-discs by 



xU-U,, 



Fii;. 453.~A.rgulus foliaceus, young nuilc. aj, antenuulc ; ti2, antenna; ah. abdomen; 

 ''1 — ^4) thoracic feet ^<.L digestive glands connected with intestine ; kfl, anterior or suctorial 

 feet ; i/2, ijosterior or leg-like portion of second raaxillai ; pa. paired eye ; r. rostrum : sd. sliell- 

 gland ; St. stylet ; ts. testis ; ua, median eye. (From Lang's Comparalive Anatomy/.) 



which the parasite clings to the surface of its host, and there are four pairs of 

 swiniining-feet (hi —hjf). Alone among the Copepoda the Branchiura have no 

 egg-sacs, and they are exceptional also in the possession of compound eyes (jja. ). 



The most familiar examples of the Eucirripedia are the Barnacles 

 found on ships' bottoms, piles, &c., and the Acorn-shells or Sessile 

 Barnacles, which occurin immense numbers on rocks between tide- 

 marks in all parts of the world. 



The common Barnacle {Lepas anatifcra?) is attached by a long 

 stalk or peduncle (Fig. 454, A., pi), covered with a wrinkled skin, and 

 bearing at its distal end the body proper enclosed in a sort of 



