DISTRIBUTION OF ORGANISMS. 153 



The necessity of taking liberal views of the procedure of 

 nature in the development of the organic world, is im- 

 pressed upon us by a character found in the very first 

 order of the articulata to which our attention is called. That 

 the Annelides (worms) are the humblest of the articulate 

 animals there is now no doubt ; yet, unlike their superiors, 

 almost all of them have red blood, a feature of the highest 

 sub-kingdom. Four leading forms in this class are described. 

 Of the Tubicolida, or those inhabiting tubes, the serpula is 

 an example. It forms for its habitation, usually upon some 

 sea-immersed stone, an irregularly twisted calcareous tube, 

 out of which it presents, floating in the water, a fan-like 

 branchial apparatus of beautiful colours. The second order, 

 Suctoria, is represented by the well-known leech ; the third 

 by the earth-worm ; the fourth by the sea- mouse (aphrodita). 

 In all of these groups, we see distinct advances in organiza- 

 tion, and this is traceable in some in an interesting confor- 

 mity with changes of scene and mode of life, from fixed situa- 

 tions to free movement in the sea, from thence to the shore, 

 and thence again to the land. From the iJfais, a simple 

 marine worm which at the recess of tide burrows in the sand, 

 there is a clear passage to the common earth-worm, which 

 adopts a similar retreat on land, and comes to the surface 

 when rain is falling. The fourth order, Dorsibranchiato, so 

 called because of gill tufts ranged along the back, have an 

 equally clear affinity, implying ancestral relationship to cer- 

 tain land animals, which, however, naturalists at present 

 regard as an independent class. The nereis, a well known 

 dorsibranchiate, is an animal of great length, composed of a 

 consecutive series of rings, each having a couple of processes 

 at each side, which are used as oars for propelling the body 

 through the water. One species is four feet long, and consists 

 of several hundred segments. By conversion of the water- 

 breathing apparatus into one fitted for aerial respiration, an 

 increase of firmness and density to the external integument, 

 and the development of a couple of limbs for each ring of the 

 body, we see the nereis, as it were, transmuted into the 



