28^ 



CRUSTACEANS. 



acorn-barnacle (nat. size). 



Coronula, or coronet-barnacles, attach themselves to the skin of whales. The 



burrowing-barnacle (Tubicinella) has the same instinct. When adult it is long 



and cylindrical, 

 consisting of a 

 stout, stony rod, 

 marked with a 

 series of annular 

 ridges. This is 

 buried deeply in 

 the skin of whales, 

 sometimes pene- 

 trating as far as the blubber. 



These Cirripedes are not true par- 

 asites, inasmuch as they do not extract 

 nourishment from the animal to which 

 they are attached ; but many members 

 of the group live exclusively upon other 

 living beings, and nourish themselves at 

 their expense. One form, for instance, 

 Proteolepas, is in the 

 adult condition a 

 maggot -shaped, 

 limbless, shell - less 

 body, living within 

 the mantle-chamber 



of other members of the same order ; while the root-headed Cirripedes (Rhizocephala) 



live parasitically upon the higher crustaceans. They 



are degenerate forms, possessing neither appendages 



nor segments, the body being a mere sac, devoid of 



alimentary canal, and absorbing nutriment by means 



of the root-like processes branching throughout the 



body of the host. 



Bivalved Group, — Order Ostracoda. 



This order is a small assemblage, characterised by 

 the possession of a bivalved shell, formed from the 

 right and left halves of the carapace, and furnished 

 with an elastic hinge to separate the valves and a 

 muscle to keep them shut. The shell encloses the 

 body which is unsegmented, has a rudimentary 

 abdomen, and bears seven pairs of appendages, 

 namely, two pairs of antenna?, three pairs of jaws 

 each belonging to the head, and two of limbs attached 

 to the thorax. These limbs, however, arc stout and 

 narrow, and, as a rule, there are no special respiratory 



STALKLESS BARNACLE (nat. Size 



PARASITIC CIRRIPEDE, 



Sacculina (nat. size). 



PARASITIC BARNACLES. 



Upper Figure — Peltogaster curvatus 

 (enlarged 1| times) ; Lower 

 Figure — Xauplius larva of Par- 

 thenojoea (enlarged 200 times). 



