178 Origin of the Paired Limbs of Vertebrates 
the pectoral of Torpedo will indicate the similar nature of the fusions 
even in such distantly related forms. 
As to the later fate of these blended muscle-buds there remains yet 
some uncertainty. Firbringer, 02, and Braus, og4a, have maintained 
that from the time of fusion of the buds the muscles are dysmetameric 
and their innervation polyneurous. This supposition as to the second- 
ary polyneury of the paired fins is by no means borne out by the recent 
experiments of Goodrich, 06. The latter investigator has tested physi- 
logically the exact distribution of the branches of the spinal nerves which 
enter the fins, and he finds that in Raja each motor nerve is distributed 
to one and only one radial muscle, and that under stimulation there is 
no spreading of the impulse such as would be the case if polyneury ex- 
isted. ‘The confused plexus at the base of the fin must then, as Good- 
rich observes, embrace only the sensory nerves, while the motor nerves 
pass through the plexus without losing their individuality. The muscles 
after fusion must, therefore, again separate without losing their haplo- 
neurous condition, at least as far as the motor nerves are concerned. 
Goodrich has even ventured the suggestion (06) that this fusion is 
not a fusion of muscle-buds involving embryonic muscle-tissue at all, 
but that what has been supposed to be such a blending is merely the 
anlage of the sensory nervous system which, arising in this region, gives 
the appearance of the fusion of muscle-buds. We cannot subscribe to 
this opinion, however, for, by actual observation, the muscle-buds at an 
early stage may be seen to be in contact and that with such clearness as 
to leave no doubt as to the interpretation. Such fusions are of frequent, 
but very irregular, occurrence in Cestracion, and there is no apparent 
order in their arrangement. They are most abundant in the anal fin in 
which the adult muscles are blended into a confused mass, and rarest in 
the caudal where the muscles of the adult are very regularly arranged. 
Moreover, blended muscles certainly do occur in the older embryo (Fig. 
18, of the condition in the second dorsal fin of a 58 mm. embryo of 
Cestracion), and remain blended in the adult. In this case the bases of 
the muscle-bands no doubt remain fused because of the great amount of 
concentration at the base of the fin. The condition in the anal is simi- 
lar, only carried much farther in concentration. 
How are these fusions to be explained? Not, as Braus, 04a, con- 
cludes, for the purpose of accomplishing the polyneury of the fin muscles, 
since Goodrich’s experiments show that the muscles are not so inner- 
vated; and not, as Goodrich, 06, suggests, that the apparent fusions are 
rudiments of the developing sensory nerve plexus, for blending actually 
