38 „■ GILBERT 0. BOURNE. 



parts, or on parts which for other reasons offer a likeness of 

 material to begin with." 



The term " homoplasy " has passed into current use, and 

 the principle expressed by it has been freely used to explain 

 numerous large and general resemblances which have obviously 

 been evolved independently, such as the general resemblances 

 between different kinds of patelliform gastropod shells, e.g. 

 between Patella, Fissurella, Septaria, Capulus, and 

 Siphonaria, or the general resemblances of external mor- 

 phology of fishes and cetacea. But the term homogeny 

 has not been so generally accepted, and many, if not most, 

 zoologists have preferred to retain the old word homology, 

 and in so doing it is clear that many of them have failed to 

 distinguish between the two quantities contained within the 

 single term, of which the differences were so clearly pointed 

 out in Lankester's essay. For it must be evident to anybody 

 who is well acquainted with the morphological literature of 

 the last thirty years that, so far from attempting to distinguish 

 between homogenetic and homoplastic resemblances, a large 

 number of authors have shown a vast amount of ingenuity in 

 referring the most minute resemblances in the organs of 

 animals, which are certainly not very closely related to one 

 another, to homology. The most extreme instances of this 

 tendency to ascribe every resemblance, however detailed, to 

 inheritance, ignoring the possibility that similar structural 

 changes may be induced by the incidence of similar forces, 

 are to be found in the works of those authors who attempt to 

 derive the lower members of one phylum of the animal 

 kingdom from highly differentiated members of another 

 phylum. 



It is, of course, true that several of the most thoughtful 

 and best informed among contemporary zoologists have been 

 fully aware of the error lurking in the indiscriminate use of 

 the term " homology," notably Gegeubauer and Fiirbringer in 

 Germany ; Cope, W. B. Scott, E. B. Wilson, and Osborn in 

 America. It is not my present intention to enter upon along 

 discussion of this subject, which I hope to return to on a future 



