THE COASTS OF SICILY. 49 



and are provided with cirrhi, but have no feet. This 

 cannot be the case, for here are protuberances which 

 appear upon the sides of each segment, and hence 

 the embryo belongs to the group of Annelids, pro- 

 perly so called. It remains to be decided whether 

 it will traverse its native sands under the form of a 

 wandering Annelid, or whether it will be confined in 

 a narrow tube, and lead the retired life of a tubicolous 

 worm. This last doubt soon vanishes, for a small 

 tubercle now appears in front of the head, which 

 lengthens and begins to play the part assigned to the 

 extensible filaments of which we have spoken. Other 

 similar appendages soon appear by the side of the 

 former, and from that moment the animal, being 

 provided with the organs necessary to secure its 

 relations with the external world, surrounds itself 

 with a tube and begins to lead the life of a recluse. 



We see, therefore, that at each phase of its deve- 

 lopment, the special nature of the Terebella becomes 

 more distinctly characterised. We have recognised 

 successively how the embryo belonged to the great 

 division of the Articulata, then to that sub-division 

 of it in which the body is divided into segments, then 

 that it is a true Annelid, and finally that it is a tubi- 

 colous worm. Investigate it a little longer, and we 

 shall be able to recognise its genus and its species. 

 This is very much the same, as if being interested in 



Thus the type of the Lumbricus and the type of the Annelid 

 mutually replace one another according to the nature of the waters 

 in which they live. These animals constitute corresponding terms 

 to one another in nature as well as in our classifications ; they are 

 the Geographical Analogues of each other. 

 VOL. II. E 



