DEGRADATION OF ORGANISATION 87 



their nervous system is characterised like the animals of the three 

 following classes by a ganghonic longitudinal cord. They have more- 

 over jointed arms with a horny skin and several pairs of transverse 

 jaws. They are therefore of lower rank than molluscs. Their fluids 

 move by a true circulation with arteries and veins. 



These animals are fixed on marine bodies and in consequence carry 

 out no locomotion ; their principal movements are those of their arms. 

 Now although they have a mantle hke the molluscs, nature coidd not 

 obtain from it any assistance for the movements of their arms, and 

 was forced to create in the skin of those arms fulcra for their muscles. 

 Hence the skin is coriaceous and almost horny like that of crustaceans 

 and insects. 



ANNELIDS. 



Animals with elongated annulated bodies without jointed legs, breathing 

 by gills and having a circulatory system and a ganglionic longi- 

 tudinal cord. 



The class of annelids necessarily comes after that of cirrhipedes, 

 because no anneUd has a mantle. We are moreover compelled to place 

 them before the crustaceans, because they have no jointed legs and it 

 would not do to interpose them in the series of those which have ; nor 

 does their organisation permit us to place them lower than the insects. 



Although these animals in general are still very httle known, the 

 rank to which their organisation entitles them proves that in their case 

 again the degradation of organisation is continued ; for from this 

 aspect they are inferior to the molluscs in that they have a ganghonic 

 longitudinal cord ; they are inferior also to the cirrhipedes, which 

 have a mantle hke molluscs ; and the fact that they have not jointed 

 legs prevents us from interposing them in the series of those which 

 are so organised. 



Annehds owe their elongated form to their habits of hfe, for they 

 either hve buried in damp earth or in mud or actually in the water, 

 mostly in tubes of various materials which they enter and leave at 

 will. Thus they are so like worms that all naturahsts hitherto have 

 confused the two. 



Their internal organisation shows a very small brain, a ganghonic 

 longitudinal cord, arteries and veins in which circulates blood that is 

 usually coloured red ; they breathe by gills, sometimes external and 

 protruding, and sometimes internal and hidden or invisible. 



