346 Introductio7i to Ariwial Morphology. 



4th. Rhizocephala {F. Miiller) — Suctoria {Lilljeborg) ; 

 parasites on the abdomen of crabs ; adults mouthless, saccular, 

 elongated (Peltogaster), or transversely elliptical (Sacculina), 

 membranous, filled by the ovary and testes, which appear ta 

 communicate ; the end of the oviduct dilates into a brood 

 pouch ; the digestive canal has vanished (Sacculina has an 

 oesophagus) ; foot-like tubes (modified antennae or cement 

 ducts) spring from the head and penetrate to the liver and 

 intestine of the host. The larva is a tailed Nauplius, which 

 develops a mantle and head tubes ; then the nauplian feet 

 are lost, and six pair of abdominal feet developed, which are 

 finally lost. These are Cirripedes degraded by parasitism. 

 In Thompsonia the larva seems to pass the nauplius stage in 

 the ^%%, from which it starts as a two-eyed Cypridine larva 

 {Semper). 



CHAPTER XLI. 



SUB-CLASS 2. — COPEPODA [M. Edwards). 



Crustacea with a cephalothorax, a pair of jaws, two 

 pair of maxillipedes, and one or two of abdominal 

 feet, some of which abort in the parasitic forms ; gills- 

 none, or leaf-like, abdominal appendages (Caliginae). 

 The free forms have movable and palpiferous man- 

 dibles, and two pair ofantennse, the anterior of which 

 become rudimental in the parasitic species. The in- 

 testine is simple and straight. The sex-organs open 

 on the fifth abdominal segment at each side, and the 

 spermaphores are flask-like and left adherent to the 

 mouth of the oviduct, where they remain even after 

 they are emptied. The young begin life as Nauplii, 

 the anterior pair of limbs becoming antennae, the 



