226 ANNALS OF SCOTTISH NATURAL HISTORY 



case, 1 the author simply states that in his example there 

 occurred " an extreme abrogation of the spinal column, 

 resulting from the coalescence of numerous vertebral 'centra." 1 

 His idea of the mode in which the coalescence took place 

 is developed in another sentence, where he states that 

 the " sixteenth and seventeenth [vertebrae] are likewise 

 anchylosed." Dr. Cobbold apparently regarded ankylosis, or 

 the pathological adhesion of the ends of the centra, as the 

 cause of the abnormal internodes. And as such as the 

 result, say, of inflammation the malformation must be 

 regarded simply as an accident in the development of the 

 individual, in other words as an environmental variation. 



But this view is untenable, for not only are no traces 

 of morbid secretions of ankylosing bone observable, but 

 there is no reason to suppose that the abnormal internodes 

 were ever separate bodies, for certainly they show no traces 

 of any pre-existing segmentation. It would, however, be 

 impossible in the course of this short notice to discuss the 

 probable causes of the aberrancies. It will suffice to state 

 that " centra [the arch-centra of bony fishes] are absolutely 

 and directly dependent upon the existence of arcualia, and 

 the cartilage of these arcualia themselves is produced by 

 and in the skeletogenous layer," and that it was in those 

 earlier parts which foreshadowed the existence of centra, 

 and not in the centra as fully developed, that the derange- 

 ment occurred. Further, since the full complement of 

 neural arches is present, the full complement of arcualia 

 may be assumed. Therefore the possibilities seem to range 

 themselves round these alternatives : (i) That certain of 

 the arcualia did not give rise to the usual skeletogenous 

 tissue within which the ossification of the centra proceeds, 

 and that, therefore, certain of the potential centra never 

 actually existed ; that is to say, each of the abnormal 

 internodes in the vertebral column of our specimen is a true 

 centrum to which one or two neural arches, properly belonging 



1 T. S. Cobbold, ' Description of a Malformed Trout, with Preliminary 

 Remarks,' " Edin. New Phil. Journ.," vol. Ixxiii., pp. 238-242, and plate. 

 Edinburgh, 1855. 



2 H. Gadow and E. C. Abbot, 'On the Evolution of the Vertebral 

 Column of Fishes,' "Phil. Trans. B.," vol. clxxxvi., 1895, P- 1 9- London, 

 1896. 



