50 ROTATORIA. 



hooks for attachment to submarine substances. The six hind 

 pair of limbs are used for swimming. The shell is not made up 

 of simple layers, as in the Mollusks, but is traversed by a corn- 

 plex series of canals, through which nourishment is conveyed. 



The Cirripedes are divided into two principal groups, the 

 pedunculated and the sessile, both of which are widely distributed 

 by ships, floating wood, sea-weed, mollusks, turtles, whales, etc. 



I. CAMPYLOSOMATA, (Gr. xaftnvkog, kampulos, curved ; crwoa, 

 soma, body.) The division contains the pedunculated forms, 

 that is, those which are furnished with stems, (Plate XVI. fig. 

 4A,) by which they attach themselves to wood or other ob 

 jects, among them are the Anatifa, (Lepas,) COMMON BARNA 

 CLE, consisting of five pieces, of which two are large valves, 

 somewhat like those of a muscle ; two smaller are articulated to 

 those near the point ; and one unites the valve along the back 

 edge ; and thus they envelop the whole of the mantle. Barna 

 cles often adhere to-the bottoms of ships in such numbers as to 

 impede their sailing. 



II. Acamptosoma, (Gr. &xa t urcTog, akamptos, uncurved ; crwwa, 

 body.) This section includes the sessile or unpedunculated forms. 

 It is represented by the Balanus, (Lat. acorn,) or ACORN-SHELL, 

 (Plate XVI. fig. 4B,) so named from its resemblance to the acorn, 

 it being short and conical in form. The mouth is protected by 

 an operculum, consisting of two or more valves. These animals 

 are found in great numbers on rocks and piers along the coast. 

 The species B. psittacus, (a parrot,) is quite large; it is eaten 

 by the natives of Chili. The Coronula attaches itself to the backs 

 of whales, imbedding itself in the skin. 



FIFTH ORDER. ROTATORIA, or ROTIFERA. Wheel-bearing 

 Animalcules. 



This order includes animalcules not to be distinctly perceived, 

 except with the microscope. They receive their name from 

 peculiarities of structure, and are wonderfully minute, some of 

 them being less than the five-hundredth part of an inch in length. 

 Nearly all of them are aquatic in their habits; their bodies are 

 transparent; hence, their general structure can, with the help of 

 the microscope, be easily recognised. They have usually an 

 elongated form, similar on the two sides ; and at the front ex 

 tremity are one or two rows of vibra-tile cilia, usually arranged 

 in a circular manner, which, when in motion, appear like re 

 volving wheels. The posterior extremity is prolonged into a 

 tail, possessing three joints, each of which has a pair of prongs 



