172 AFFINITIES AND GEOGKAPHICAL 



habitation, usually upon some sea-immersed stone, an irregu- 

 larly 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 organization, and this is traceable in some in an 

 interesting conformity with changes of scene and mode of life, 

 from fixed situations to free movement in the sea, from thence 

 to the shore, and thence again to the land. From the Nais, 

 for example, 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, 

 Dorsi-branchiata, so called because of gill tufts ranged along 

 the back, have an equally clear affinity, implying ances- 

 tral relationship to certain land animals, which, however, 

 naturalists at present regard as an independent class. The 

 Nereis, a well-known dorsi-branchiate, 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 con- 

 version 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, trans- 

 muted into the Myriapod. 1 Here, however, there may be 

 more than one line of passage ; for the two great families of 

 the myriapods, the lulidae and Scolopendridae, are diverse in 

 character, the former being vegetable feeders, the latter carni- 

 vorous, and it appears as a rule in the genetic system, that true 

 carnivores are always apart. Confining our view to the Scolo- 

 pendridae, we see a remarkable continuity of character and 

 habits transmitted to them from the presumed marine ancestor 

 (nereis), allowing for the altered medium of existence. The 

 scolopendra is an animal furnished with powerful destructive 

 organs ; and, living under stones and the bark of trees, and in 

 fissures generally, it is his custom to wind insidiously along, 

 and dart upon any little animal which comes in his way. Of 

 the nereides, on the other hand, we are told that they " usually 



1 See the presumed steps of conversion fully described in Professor 

 Tlymer Jones's Animal Kingdom, p. 224. 



