72 ARTHEOPODA. 



The posterior extremities consisting of a rudimentary abdomen, 

 thorax, and six pairs of many-jointed limbs, which are used for 

 capturing its food. They have no heart. 



When the sexes are separate, the males are Yery minute and 

 epizoic on the females ; they are very rudimentary, mere sperm- 

 sacs, and their characters are valueless for classification. 



The metamorphosis of the Cirripedia is very complex, but in 

 the earlier stages the larva? resemble the Entomostraca (Nauplius, 

 Cypris). Darwin divides them into three orders, to which Glaus 

 adds the Ehizocephala. Schmarda retains the latter in the 

 Epizoa (Ichthyophthira). 



Body unsegmented EHIZOCEPHALA. 



Body segmented. 



Without limbs APODA. 



With limbs. 



Limbs abdominal ABDOMINALIA. 



Limbs thoracic THORACICA. 



Order I. EHIZOCEPHALA. 



SUCTORIA. 



Body cylindrical or sac -shaped, without segmentation. No 

 limbs, organs of sense, nor intestine. 



There are two openings into the body, one serving as a mouth, 

 the other as an anus. The reproductive organs are well deve- 

 loped. 



These are sac-like or disciform parasites on crabs, to which 

 they attach themselves by root-like tubes [modified antennas] pro- 

 ceeding from the anterior portion of the body, penetrating and 

 intertwining themselves into the substance of their victim. Crabs 

 infested with Sacculina are barren, at first mechanically, after- 

 wards histolcgically. Peltogaster is parasitic on the abdomen of 

 Paguridse. An opinion has been expressed that the Peltogaster 

 of the Pagurus has become a Sacctilina on the crab. 



The young pass through a Nauplius and a Cypris stage. 



Sacculinidee. Peltogastridce. 



Sacculina=Pachybdella. Peltogaster. 



Clistosaccus. Apeltes. 



Lernaeodiscus. Sylon. 



