GREGORY: FISH SKULLS 95 



Remarks on Dr. Leighton Kesteven's Nomenclature 



In numerous papers Dr. Leighton Kesteven has conducted a painstaking and extensive 

 investigation on the morphology of the teleost skull. In this he proposes many radical 

 alterations in the long accepted homologizations of the elements of the fish skull with those 

 of higher vertebrates, including man. For instance, he comes to the conclusion that the 

 homologues of the human premaxilla and maxilla are to be sought not in the premaxilla 

 and maxilla respectively of teleosts but in the vomer and palatine of teleosts; also that 

 either the quadratojugal or the jugal of super-piscine vertebrates is represented by the 

 so-called pterygoid of teleosts. Accordingly he changes the names of the fish premaxilla 

 and maxilla to "premaxillary labial" and "maxillary labial" respectively; the vomer be- 

 comes the " premaxilla," the palatine, the " maxilla," while the pterygoid is called " quadrato- 

 jugal." 



I regret that I cannot accept these and similar conclusions of Dr. Leighton Kesteven's, 

 first, upon broad grounds and secondly, in consideration of the merits of each case. 



First, as to generalities. Our author's methods of investigating the problem of equating 

 the elements of the teleost skull with those of higher vertebrates, including man, are, it is 

 true, not essentially different from those of W. K. Parker, Huxley, Owen and most later 

 morphologists, so that he is not to be criticized harshly for following in the well worn track. 

 That time-honored method, against which I have protested for many years past, Is essen- 

 tially this: that if one is seeking to establish the homologies of a given element in a member 

 of one class of vertebrates with a similar appearing or similarly situated element in a mem- 

 ber of another class of vertebrates, one may do so by comparing single pairs of forms chosen 

 at will by the investigator, without regard to the magnitude of the phylogenetic gap between the 

 members of each pair; further, that if in any such pair a given element in one is matched by a 

 similar appearing element in the other, the tzvo elements are assumed to be homologous without 

 further inquiry as to whether the similar appearances may not be examples of analogy rather 

 than of homology. 



This ancient method has immense apparent advantages over what I conceive to be 

 the only reliable method of tracing homologies, in particular between members of different 

 classes. First, it has always enabled morphologists (including embryologists) to write 

 papers on the homologies and evolution of any particular organ without having to bother 

 about the whole vast and complex background of the classification and evolution of the 

 animals used in the comparison, without considering the palasontologlcal history of the 

 forms, without inquiry as to the evidence of changes In habits and correlative changes in 

 structure, as affecting the position and appearance of the part or organ under investigation. 



Secondly, as one can disregard the vast numbers of known living and fossil animals that 

 bear the part under investigation, one can also conveniently limit his comparisons to almost 

 any few forms that happen to be at hand. 



Thus, hypothetical "phylogenies" of organs have been constructed as if they were en- 

 tirely independent of the phylogenies of the animals that carried those organs. 



For example, Leighton Kesteven (1926a, pp. 132-139) uses the conditions of the maxillse 

 in the eels for the identification of these bones in the fishes generally, thus ignoring the 

 extreme specializations of the eels (see p. 202 below) which render them peculiarly unsuitable 

 as a starting point for the establishment of homologies of their jaw elements with those 

 of tetrapods and man. 



