ARTHROPODA. 37 



2. Order Stomapoda. 



53. A Stomapod (Squilla mantis'), dissected to shew the 

 same parts. 



The double ' commissural cord T connecting the prse-oral with 

 the post-oral ganglion is remarkably well seen. The remaining 

 thoracic ganglia supply the thoracic legs. The abdomen con- 

 tains six ganglia, each of which gives off two or more nerves 

 on each side to supply the muscles of its segment. The longi- 

 tudinal commissural cord connecting the different ganglia is 

 more or less distinctly double throughout. 



Sub-Class CIRRIPEDIA. 



54. A Barnacle (Lepas anatifera). 



The body of the animal consists of 'capitulum' and 'peduncle.' 

 The peduncle is soft and fleshy, and invested externally with a 

 tough rugose skin, which by its distal, clavate extremity serves 

 to attach the animal. The 'capitulum' is somewhat triangular, 

 consisting of two lateral valves, strengthened externally by 

 several calcified plates, and encloses the major part of the body 

 of the organism. The calcified pieces composing the valves are 

 four in number, two in each valve. The superior or distal 

 plates are called ' terga,' and the lower or proximal plates, also 

 the largest, are called 'scuta.' The two valves are connected 

 with each other along one side, through the intermediation of a 

 mesial curved piece, the ' carina.' Within those valves the body 

 of the animal is to be seen : its dorsal surface in relation with 

 the inner surface of the ' carina/ The body consists of a ' prosoma' 

 which includes the cephalic segments of six thoracic segments 

 and a tubular extension from the hinder edge of the last 

 thoracic segment, which functionally is a penis, but morphologi- 

 cally may be the aborted representative of the abdomen, or 

 post-abdomen, of other Crustacea. The mouth is bounded 

 anteriorly by a tumid, transversely extended labrum. Behind 

 this we find, first, a pair of mandibles, each armed with a setose 

 palp, and two pairs of maxillae. Six pairs of appendages are 

 attached to the thorax, each consisting of a basal 'protopodite' 

 terminating clistally in a long multiarticulated 'exopodite' and 

 'endopodite.' That part of the body which lies in front of the 



