6 INTRODUCTION. 



primordial valves : these are not calcified ; they are formed 

 at the first exuviation, when the larval integuments are 

 shed : in mature Cirripedes they are always seated, when 

 not worn away, on the umbones of the valves. 



The membrane connecting the valves, and forming the 

 peduncle, and sometimes in a harder condition replacing 

 the valves, I have often found it convenient to designate 

 by its proper chemical name of Cldtine, instead of by 

 horny, or other such equivalents. When this membrane 

 at any articulation sends in rigid projections or crests, for 

 the attachment of muscles or any other purpose, I call 

 them, after Auclouin, apodemes. For the underlying true 

 skin, I use the term corium. 



The animal's body is included within the capitulum, 

 within what I call the sack (see PI. IV, figs. 2 and 8' a, and 

 PI. IX, fig. 4). The body consists of the thorax supporting 

 the cirri, and of an especial enlargement, or downward 

 prolongation of the thorax, which includes the stomach, 

 and which I have called the prosom a. (PI. IX, fig. 4n). 

 The cirri are composed of two arms or rami, supported 

 on a common segment or support, which I call the pedicel. 

 The caudal appendages are two little projections, either 

 uni- or multi-articulate (PI. IV, fig. 8' a), on each side of 

 the anus, and just above the long proboscis-like penis. 

 On the thorax and prosoma, or on the pedicels of the 

 cirri, there are in several genera, long, thin, tapering 

 filaments, which have generally been supposed to serve 

 as branchiae ; these I call simply filaments, or filamentary 

 appendages (PL IX, fig. 4<g — /). The mouth (fig. 4 b) is 

 prominent, and consists of palpi soldered to the labrum ; 

 mandibles, maxillm, and outer maxilla, these latter serve 

 as an under lip ; to these several organs I sometimes 

 apply the title used by Entomologists, of " trophi." 

 Beneath the outer maxillae, there are either two simple 

 orifices or tubular projections ; these, I believe, serve as 

 organs of smell, and have hence called them the olfactory 

 orifices. Within the sack, there are often two sheets of 

 ova (PL IV, fig. 2 b), these I call (after Steenstrup, and 



