PHYLUM ARTHROPODA 



577 



permanently attached like the degenerate forms just described, but crawling 

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

 cephalo-thorax, and a small bilobed abdomen (a&.). The mandibles and maxilla? 

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

 is a median tube ending in a spine (st.). The second maxilla? are divided into 

 two portions, the anterior of which (kf-1) are modified into sucking-discs by 



Fn.. 403. Argulus foliaceus, young male. ], anteniuile ; 03, antenna; ab. abdomen; 

 bl 64, thoracic feet ; d. digestive glands connected with intestine ; Lfl, anterior or suctorial 

 feet ; kJ2, posterior or leg-like portion of second maxilla; ; pa.' paired eye ; r. rostrum : ad. shell- 

 gland ; st. stylet ; tg. testis ; tt, median eye. (From Lang's Comparative Anatomy.) 



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

 swimming-feet (bl 6^). Alone among the Copepoda the Branchiura have no 

 egg-sacs, and the}' are exceptional also in the possession of compound eyes (pa. ). 



The most familiar examples of the Eucirripedia are the Barnacles 

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

 Barnacles, which occur in 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,_/?), covered with a wrinkled skin, and 

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



