OCT. 1895. VERTEBRAL COLUMN OF AMIA HAY 43. 



composition of any of them ? I am not able to answer definitely. I 

 am not aware that anything like intercalated cartilages has been found 

 in any of our bony fishes belonging to the group of Teleosts. The 

 Clupeidce, as being most closely related to the Ami idee, might be ex- 

 pected to throw light on the question. In case that the cartilages 

 forming the upper arms of the cross found in the vertebrae of some 

 fishes, as Lucius (sox), were segmented off from that contained in 

 the remainder of the upper arch, I should regard it as representing 

 the pleurocentrum ; but I find mention of only one fish showing such 

 a condition. This is the genus Monacanthus, referred to by Goette 

 (33, p. 129). Usually the cartilage of the upper arch comes down on 

 the notochord, and is unbroken from end to end, as it seems to be in 

 Lucius and Salmo. It may be that in these the pleurocentrum is 

 wholly missing. 



I do not think that there can be any question that the lower por- 

 tion of the osseous ring which encircles the notochord and forms the 

 earliest rudiment of the centrum is the hypocentrum, Does this 

 give origin to all the bone which enters into the centrum ? If so, the- 

 opinion of Prof. Cope is correct. The statements of Lotz, Cartier, 

 and Goette that the primitive vertebral ring grows from the points 

 of contact with the notochord iipward and meet above the notochord, 

 are in favor of this idea. If, on the other hand, bony centers, how- 

 ever small, should be found at the bases of the upper arches, the ver- 

 tebra would not be wholly a hypocentrum. And this, I suspect, will 

 be found to be the case. If those observations are correct which go 

 to prove that the ring starts at four points, the fishes in which this 

 happens would have something more than hypocentra. If no pleu- 

 rocentra are developed, the centrum would be formed from the bases 

 of the upper and the lower arches, and be similar to those of the 

 middle tail region of Amia which are furnished with arches. It is 

 extremely probable that our modern bony fishes are derived from 

 many distinct sources among the ancient Ganoids, and it is possible 

 that among the latter were some which never developed bony inter- 

 vertebral elements. And even among the relatives of Amia there were 

 some, like Hypsocormus, which seem not to have the intervertebral 

 ossifications, possibly not the cartilages. We must therefore be pre- 

 pared to find that the composition of the vertebral centra of our fishes 

 is various. 



The ribs of Amia deserve a portion of our attention. None are 

 present in larvae i5mm. long; all have been laid down in cartilage 

 in specimens 23mm. in length. Hence I cannot, as I hoped to do, 

 make observations on the method of their origin, whether in direct 

 connection with the transverse processes or independent of them. 



