MERISTIC HOMOLOGIES IN VERTEBRATES 



J. S. KINGSLEY 



One of tlie most difficult problems in vertebrate morphology 

 is to explain the serial homologies between the different groups. 

 In the lower segmented animals these difficulties, although they 

 exist, are far more simple and are far more easily explained. Thus 

 no one has any doubt that the tenth or the fifteenth somite of 

 Homarus is the exact equivalent of the serially homologous somite 

 of Cancer. Between the larger Arthropodan divisions the task 

 of comparisons of somites is possibly not so easy yet all attempts 

 at drawing homologies between, say, a hexapod, an arachnid and a 

 crustacean, are based upon the assumption of exact serial equiv- 

 alency. It is true that one author or aiiotlier has at times sug- 

 gested the possibility of intercalation or t^lision of a somite, but 

 these have been mere suggestions and liavc usually been discarded 

 in the discussions. 



are forced to assume that the slioul.lcr -inllc and f.'iv liml.cf ttir 

 frog are the lionioh.oues of those of man. allhou-h their eoiuiee- 



taken into account. In the ease of the i)elvie arch the numeri- 

 cal disparity of the corresponding somitt^s is even ureater, but in 

 either case the identity of structure of arcli and limb is so great 

 that doubt of homology is praerieally impossible. How then has 

 it come about that say the twelfth somite of the Am])hibian is not 

 homologuc of the twelfth but of more nearly the twentieth of 

 man? 



In Gegenbaur's hypothesis that the oinlhvs are derived from 

 branchial arches and that thtvse have migrated backwards over 



problems of the relations of -inile. f.I bo.lv srp.'ents. The back- 

 ward nuVration has been arreted at dillerent points in tli^- various 



