No. 3-] THE VERTEBRAL COLUMN OF FISHES. 135 



and its apex into the interdorsal, we are not told. We can, it 

 seems to me, know this only in case the two structures occupy 

 the same area. But I do not believe that the basiventrals do 

 occupy the same areas that the ventral sklerotomes occupied. 

 It seems to be accepted that the arches, upper and lower 

 (basidorsals and basiventrals), are placed, primitively at least, 

 opposite to or in the septa between the myomeres, while the 

 intercalated cartilages (interdorsals and interventrals) lie oppo- 

 site the myomeres themselves; but if the views of Gadow and 

 Abbott are correct, the very opposite is true. The basalia 

 would be myomeric; the interbasalia, intermyomeric. (See 

 diagrams on page 188.) The authors hold that the skleromeres 

 alternate with the myomeres, and that the ribs, like the inter- 

 muscular septa, are intermyomeric, and they account for this 

 by the peculiar manner of fusion of the sklerotomes; but their 

 explanation assumes the myomeric position of the bases of the 

 skleromeres and their resultant basalia. We have no reason 

 for believing that the neural arch grows out of the upper an- 

 terior angle of the skleromere and the rib out of the lower 

 posterior angle. 



On the whole, since the materials composing the sheath of 

 skeletogenous cells that surround the notochord do certainly 

 all fuse, so as to be devoid of all segmentation, it is easier to 

 believe that, when differentiation leads to the formation of car- 

 tilages, the basalia are constituted out of cells that were derived 

 partly from the protovertebra in front, partly from the one next 

 behind. 1 It is difficult to see why the adjacent edges of two 

 dorsal sklerotomes should not be as likely to remain in perma- 

 nent fusion as the ventral sklerotome of one protovertebra 

 with the dorsal of another. 



In their study of Amia, Dr. Gadow and Miss Abbott have 

 come to conclusions in many ways different from those reached 

 by myself. Indeed, I am obliged to antagonize most of the 

 statements made by these writers. As regards materials, my 

 own appear to be much more complete. So far as I can dis- 

 cover from their paper, they possessed no specimens smaller 



1 We must keep in mind the possibility that the cartilage cells are, or are de- 

 rived from, immigrants from some outside region. 



