CHAP. XI. EVOLUTION. 113 



not see, and it may therefore find a place here. Three 

 years ago I found on the walls of one of my glasses some 

 small worm-tubes (fig. 65), the inhabitants of which bore 

 three pairs of barbate branchial filaments, and had no 

 operculum. According to this we should have been 

 obliged to refer them to the genus Pr'otula. A few 

 days afterwards one of the branchial filaments had be- 

 come thickened at the extremity into a clavate oper- 

 culum (fig. 66), when the animals reminded me, by the 

 barbate opercular peduncle, of the genus Filograna, 

 only that the latter possesses two opercula. In three 

 days more, during which a new pair of branchial fila- 

 ments had sprouted forth, the opercular peduncle had 

 lost its lateral filaments (fig. 67), and the worms had 

 become Serpulce. Here the supposition at once pre- 

 sents itself that the primitive tubicolar worm was a 

 Protula, that some of its descendants, which had 

 already become developed into perfect Protulce, subse- 

 quently improved themselves by the formation of an 

 operculum which might protect their tubes from 

 inimical intruders, and that subsequent descendants 

 of these latter finally lost the lateral filaments of the 

 opercular peduncle, which they, like their ancestors, 

 had developed. 



What say the schools to this case ? Whence and 

 for what purpose, if the Serpulce were produced or 

 created as ready-formed species, these lateral filaments 

 of the opercular peduncle ? To allow them to sprout 

 forth merely for the sake of an invariable plan of 

 structure, even when they must be immediately re- 



