36 DEVELOPMENT OF THE SYSTEMIC LYMPHATIC VESSELS 



persistence and further development of the cardinal collateral 

 veins. In other words, not a single individual in the entire series 

 possessed a marsupial postcava, although every shade in the possi- 

 ble range of variation in the district of the post- and supracardinal 

 lines was represented by numerous examples. Thus with an ab- 

 dominal venous organization of very unstable equilibrium, as shown 

 by the large percentage of cardinal variants, 24 the cat yet keeps 

 entirely within the district of the common genetic ground plan 

 assigned to the placentalia. This phylogenetic consistency is 

 maintained in spite of the fact that, as just demonstrated in series 

 258, the embryo develops the raw materials, as cardinal collateral 

 channels, out of which a preaortic postcava of the marsupial 

 type could be evolved. In my own estimation cats possessing this 

 form of postcava may exist and may eventually be found. But 

 the failure to encounter them in the relatively large series of adults 

 already examined speaks volumes for the value of vascular organ- 

 ization in interpreting phylogenetic relations. 



In this light the postcaval development and adult structure of 

 Tragulus, for example, are of the utmost importance and signifi- 

 cance. The unprejudiced observer is often forced to wonder 

 why some exponents of palaeontological research are content to 

 draw far-reaching phylogenetic conclusions from the remnants of 

 the incomplete locomotory apparatus at their disposal, without 

 utilizing the results of modern comparative anatomical and embryo- 

 logical investigation in determining at least the mutual relations 

 of the extant forms, massed by an ironclad taxonomy into more 

 or less questionable groups, whose ancestry and derivation form 

 one of the primary problems of the palaeontologist. The case of 

 Tragulus just alluded to, the parotid complex and alimentary 

 canal of Hyrax, the amniote homologies of the derivatives of the 

 Sulcus buccalis determined by Schulte, the sharp line of lymphatic 

 demarcation recently shown by Silvester to structurally separate 

 absolutely the platyrrhine and catarrhine divisions of the lower 

 primates, these and other facts are only instances in which the 

 inadequacy of a superficial convergence of dental and skeletal 

 characters, for the purpose of establishing valid phylogenetic 

 relations, is revealed by cardinal divergence in the far more stable 

 and important organization of vascular and visceral structure 



