Morphology of the Fins 73 



" If there is any soundness in zoological speculation at all, I 

 think it must be admitted that the more primitive vertebrates 

 were creatures possessing a notochordal axial skeleton near the 

 dorsal side, with the main nervous axis above it, the main 

 viscera below it, and the great mass of muscle lying in myotomes 

 along its sides. Now such a creature is well adapted to move- 

 ments of the character of lateral flexure, and not at all for 

 movements in the sagittal plane which would be not only 

 difficult to achieve, but would tend to alternately compress and 

 extend its spinal cord and its viscera. Such a creature would 

 swim through the water as does a Cyclostome, or a Lepidosiren, 

 or any other elongated vertebrate without special swimming 

 organs. Swimming like this, specialization for more and more 

 rapid movement would mean flattening of the tail region and 

 ts extension into an at first not separately mobile median tail- 

 fold. It is extremely difficult to my mind to suppose that a 

 new purely swimming arrangement should have arisen involving 

 up-and-down movement, and which, at its first beginnings, 

 while useless as a swimming organ itself, must greatly detract 

 from the efficiency of that which already existed." 



Objections to Gegenbaur's Theory. We now return to the 

 Gegenbaur view that the limb is a modified gill-septum. 



"Resting on Gegenbaur's discovery already mentioned, that 

 the gill-rays in certain cases assume an arrangement showing 

 great similarity to that of the skeletal elements of the archip- 

 terygium, it has, so far as I am aware, up to the present time 

 received no direct support whatever of a nature comparable 

 with that found for the rival view in the fact that, in certain 

 forms at all events, the limbs actually do arise in the individual 

 in the way that the theory holds they did in phylogeny. No 

 one has produced either a form in which a gill-septum becomes 

 the limb during ontogeny, or the fossil remains of any form 

 which shows an intermediate condition. 



"The portion of Gegenbaur's view which asserts that the 

 biserial archipterygial fin is of an extremely primitive charac- 

 ter is supported by a large body of anatomical facts, and is 

 rendered further probable by the great frequency with which 

 fins apparently of this character occur amongst the oldest 

 known fishes. On the lateral-fold view we should have to 



