342 EDWIN S. GOODinCIl. 



the fin is continuous and there is no possibility of migration. 

 Longitudinal connecting nerves have long been known to 

 exist at the base of the unconcentrated fins of Teleostean 

 fish ; I find them also at the base of the dorsal fin of 

 ChiniKra; which is scarcely, if at all, concentrated. 



Objkctions to the Gill-Arcii Theouy. 



We may now deal with some very serious difficulties in the 

 way of the gill-arch theory. Firstly, it oifers no intelligible 

 explanation of the participation of a large number of seg- 

 ments in the formation of the paired fins. Yet it is always 

 the case that a considerable, and sometimes a very large, 

 number of spinal nerves and myotomes contribute towards 

 its development. 



Secondly, if the skeleton of the paired fins were derived 

 from gill-rays we should expect the muscle supply to be 

 drawn, not from the myotomes at all, but from the unseg- 

 mented "lateral-plate," or visceral, musculature, which is 

 innervated by the dorsal roots of the spinal nerves. It is true 

 that the trapezius muscle attached to the scapula is of 

 lateral-plate origin, and is supplied from the vagus nerve ; 

 yet it does not enter into the fin, does not, in fact, belong to 

 the fin musculature. At all events, in the pelvic region 

 there is no trace whatever of other than segmented muscles. 



A third, and perhaps still more important, objection to 

 Gegenbaur's theory is this : the position of the limb-girdles 

 in relation to the nerves, blood-vessels, ccelom, etc., is 

 exactly the reverse of what it should be if they 

 were derived from visceral arches. The ccelom, the subin- 

 testinal vessel (heart, etc.), the myotomes and their nerves, 

 all pass outside the visceral arches. The limb-girdles, on the 

 contrary, lie morphologically outside these structures, so that 

 the nerves frequently pass through the girdles to reach the 

 fins. In fact, the girdles lie in the outer body-wall, while the 

 visceral arches lie in the wall of the alimentary canal. No 

 mere superficial resemblance in shape of the girdle to ihe 



