26o Likenesses; or, Philosophical Anatomy 



animal be the equivalent of a series of perfectly separated 

 individuals of another kind of animal in which the process of 

 fission was completely carried through. In other words, Mr. 

 Spencer would explain the serial homology of Annulose 

 animals by the supposed coalescence (through imperfect 

 fission) of organisms of very simple structure, such as the 

 small aquatic worms called Planarice, in one aggregated 

 longitudinal series through the survival of the fittest aggre- 

 gation. This is a very ingenious speculation, yet there is- 

 positive evidence which directly conflicts with Mr. Spencer's, 

 hypothesis. Mr. Mosely, in his investigations of the land 

 Planarice of India, has brought forward evidence that a 

 single Planaria is the equivalent not of a segment of a leech 

 but of a whole leech. Yet a leech is the morphological 

 equivalent of a whole centipede, lobster, or other higher 

 Annulose animal, and therefore each higher Annulose animal 

 must be regarded as itself a morphological unit, and not an 

 aggregation of such units. 



Moreover, even lateral, vertical, and serial homology da 

 not exhaust the kinds of likeness (homologies) which have 

 arisen independently of descent. For structures are con- 

 tinually being discovered (in animals of different kinds) so- 

 strikingly alike that their resemblance would naturally be 

 taken, on the theory of Evolution, for a sign of genetic 

 affinity, and yet the circumstances under which they occur 

 preclude any such explanation. The resemblance which 

 exists between the ankle bones of such widely different 

 animals as frogs, and the small African lemurs, termed 

 Galagos, may be taken as an example of such uninherited 

 likeness. In a genus of the frog order (namely Pelohates), 

 and in the turtle, a bony expansion covers over that hollow 

 at the side of the head which is called the ' temporal fossa.' 

 A similar expansion has lately been found to exist in a 

 certain African animal of the rat order (namely Lophi(>mys\ 



