HOMOLOGY AND ITS INTERPRETATION 59 



and reproduction is mitotic cell division. This leads to the 

 production of a somatella, among the protista, and of a soma 

 differentiated by histogenesis into two or three primary 

 tissues, among the metista. All these fundamental processes 

 are strikingly uniform throughout the entire plant and animal 

 world. In these universal properties of living matter, there- 

 fore, we have a common basis for general structural and or- 

 ganizational laws, which, though irreducible to the "common 

 ancestors" of Transformism, is quite adequate to account for 

 both the homologies and analogies of living matter. Accept 

 this basis of general laws regulating the development of living 

 matter, and there is no difficulty in seeing why the problems 

 posed by exposure to analogous environmental conditions are 

 solved in parallel fashion by organisms, irrespective of whether 

 they are nearly, or distantly, related in the sense of morphol- 

 ogy. Transformism, on the other hand, can only account 

 for homology at the expense of convergence, and for 

 convergence at the expense of homology. So far as a 

 common ancestral basis is concerned, the two kinds of 

 resemblance are, from the very nature of the case, irreducible 

 phenomena. 



It is only, in fact, by surrendering the principle that simi- 

 larity entails community of origin, and by falling back on the 

 suggested common basis of general laws, that Transformism 

 makes room in its system for the troublesome facts of con- 

 vergence. "It might be reiterated in passing," says Dwight, 

 "that this 'convergence' business is a very ticklish one. We 

 have been taught almost word for word that resemblance 

 implies relationship, or almost predicates it; but according 

 to this doctrine it has nothing to do with it whatever." 

 ("Thoughts of a Cath. Anat.," p. 190.) And in a subsequent 

 chapter he says: "No very deep knowledge of comparative 

 anatomy is needed for us to know that very similar adapta- 

 tions for particular purposes are found in very diverse animals. 

 The curious low grade mammal, the Ornithorhynchus, with a 

 hairy coat and the bill of a duck, is a familiar instance. We 



