ARTICULATA. 101 
has its extremity enlarged into an operculum for closing the aperture. The 
tubes which these animals secrete are calcareous, and twisted in a very 
irregular manner. They are affixed to submarine bodies, either singly, or 
a great many in a single mass. The tubes are common in the tertiary and 
secondary formations. | 
Fam. 2. Amphitritide. In this family the indistinct head is composed 
of three segments, the thorax of not less than twelve, and the abdomen of a 
great many. The mouth has numerous prehensile tentacular filaments, 
and the tube is formed out of a mucous secretion to which extraneous 
objects, such as fragments of shells, are affixed. They live singly or 
aggregated. Amphitrite (pl. 77, fig. 18), Sabella (pl. 75, fig. 68), Zerebella 
(pl. 76, jig. 82). The genus Hermella resembles the Dorsibranchia in 
having the branchiz dorsal ; the cephalic appendages not being branchize 
but tentacles, according to Milne Edwards. 
Class 2. Cirrhopoda. 
The animals of this class are monoicous, inclosed in a hard shell or 
subgelatinous envelope, deprived of locomotive powers, and affixed to 
extraneous submarine bodies, some by a peduncle (pl. 76, figs. 51, 52), and 
others by their base (figs. 58, 54). The earlier authors placed these animals 
with the Mollusca, and the shells are often retained in conchological cabinets. 
Their articulated cirrhi and double nervous axis indicate their true nature ; 
and whilst they have been made a distinct class from the Crustacea, partly 
on account of the supposed absence of an articulate structure, Dr. St. Ange 
affirms that evident traces of such a structure exist. 
These animais undergo a metamorphosis, the young being bivalvular like 
bivalve mollusca, and capable of swimming about freely for some time before 
it affixes itself permanently. In this condition the limbs can be protruded 
from the front of the shell; the anterior pair being large, and provided with 
a sucker and hooks for attachment to submarine bodies. The six posterior 
pairs are used in swimming. The animal, at this period, bears considerable 
resemblance to the small branchiopoda. Mr. Thompson, of Cork, placed 
some of them in a vessel of sea water, and in a week’s time two of them 
had mantled and were affixed to the vessels as barnacles. A few days 
afterwards, another individual was observed to throw off its shell and affix 
itself. Both the orders of Cirrhopoda undergo these changes. 
The jaws are lateral, articulated, and toothed; the cirrhi are articulated, 
curved, and arranged along the abdomen, resembling somewhat the members 
along the lower surface of the tail in the Crustacea. The class contains the 
two orders Campylosomata and Acomptosomata, both of which are widely 
distributed by floating wood, ships, sea-weed, mollusca, whales, turtles, &e. 
Orper 1. Campyiosomata. This order contains the pedunculated 
flattened forms like Aftella (Oken, 1815; Pollicipes, Leach, 1817, pl. 76, 
fig. 51), and Lepas (Linn., 1748; Anatifa, Brug., 1792, pl. 76, fig. 52), in 
which the shell is generally composed of two large lateral triangular basal 
ICONOGRAPHIC ENCYCLOP£ZDIA.—YVOL. II. 20 305 
