38 Traces of Unity in the Appendicular 



portion, topped by two hollow nipples, out of each 

 of which may be protruded a tuft of barbed setae 

 or bristles, which are at once effective organs of loco- 

 motion and formidable weapons. These two projec- 

 tions are distinguished by their position as the dorsal 

 branch and the ventral branch, and by some other peculi- 

 arities as well. The dorsal branch, which is the larger of 

 the two, carries a certain lamelliform process to which the 

 name of elytra is given, as well as a tolerably long palp 

 or cirrus, and a number of thread-like processes, which 

 seem to have a branchial office : the ventral branch 

 may have the cirrus and the threads, but usually it has 

 neither. This setigerous foot is often called pied-a- 

 elytre. When the elytra is absent, as it often is in many 

 congenerous forms, the name given to it is as often pied- 

 sans-elytre. And in these pieds-sans-elytres it is that 

 the relations of the elytrae, and of the hairy processes 

 near them, as well as of the cirri, to branchiae, come 

 out most palpably ; for on comparing the feet in con- 

 generous forms of life it is evident that the branched 

 dorsal tufts of the sand or lug-worm (arenicold), which 

 is so favourite a bait with salt-water fishermen which 

 tufts are unmistakeable branchiae or gills are only 

 modifications of the elytra and of the neighbouring 

 hairy processes in the common aphrodite, while at the 

 same time it is generally evident, that the analogous 

 hairy processes, as well as the cirrus of the ventral 

 branch of the setigerous foot may also undergo a similar 

 transformation into true branchiae. These parts, no 

 doubt, are too rudimentary to make it possible to be 

 very dogmatic in interpreting them, but this is plain, 

 that they show a marked disposition to that two-fold 

 division which is so conspicuous in the cirripedia, and 

 that, while each of the branches may take upon itself a 



