296 Professor MacGillivray on the Cirripedia 
mouth, represent the thoracic feet of the crustacea ; the rest may be 
considered as analogous to their abdominal false feet. The intestinal 
canal has two apertures; the oral with a prominent arched lip, a 
pair of palpi, and three pairs of maxillary appendages, expanded 
and ciliate at the end; the anal subterminal and dorsal; the ceso- 
phagus is short; the stomach large, with bursiform appendages ; 
the intestine wide. They have a complete double circulation, with 
white blood, and respire by branchiz, varying in form, but usually 
placed at the base of the lower cirri. Their nervous system is com- 
posed of a double series of ganglia, as in the crustacea. They have 
no distinct head, eyes, or tentacula. The individuals are bisexual ; 
the ova are fecundated in their passage, and escape by a long, very 
slender, contractile tube, placed at the extremity of the body, be- 
tween the last two pairs of cirri. 
In some, the envelope or tegmen is composed of several calcareous 
pieces, disposed in two lateral plates, with a medial or dorsal piece, 
or of a membranous or coriaceous epidermic covering, in which are 
developed small or rudimentary calcareous pieces, together with a 
flexible, and somewhat contractile peduncle. In others it is mem- 
branous, with four or two lateral pieces at the top, and inclosed ina 
calcareous conical tube, composed of six or fewer contiguous or united 
pieces, open above, and closed below by a membranous lamina or a 
calcareous plate. The mantle in all is open above, in the form of a 
slit, by which the cirri may be protruded. 
These cirri are constantly in rapid motion, and are the means of 
impelling the water into the cavity between the body and the man- 
tle, both for respiration, and as containing the animal matters on 
which they feed. The body is affixed to the tegmen or shell by a 
transverse muscle, placed at its lower part, and by muscular fasci- 
culi, which spread over the mass of the viscera. 
The young, at first free, locomotive, and resembling the larve of 
certain crustacea, undergo various changes, both before and after they 
become fixed. But, as in these notes, I intend to confine myself 
exclusively to what I have personally examined, I ain unable at pre- 
sent to say anything on this subject. 
These animals, all of which inhabit the sea, are naturally ar- 
ranged into two orders, Pedunculata and Sessilia, each of which 
contains a single family, 
The Crrrirep1a Pepuncunata, commonly named Barnacles, have 
the body supported by a tubular, fleshy, somewhat contractile and 
extensile peduncle, of which the base is attached to some firm sub- 
stance. To this series belong the genera Lepas, Cineras and Otion, 
which; with others, form the family of the Lepadina. 
In it the animal is oval or oblong, generally compressed, very con- 
vex on the back, narrowed behind, suspended in a testaceous or 
membranous envelope, to which it adheres by a transverse muscle, 
