NOTES ON MEDIAN AND PAIRED FINS OF FISH. 339 



root. In fact, it seems to be very probable indeed tliat, even 

 in the adult, tlie radial muscles are strictly segmental and 

 haploneurous (see below, pp. 364-371). Some fusions may 

 take place, some disturbances of the metameric order may 

 occur, especially at the extreme anterior and posterior ends of 

 the fins; but it is quite firmly established that each adult radial 

 muscle develops from, and corresponds iu position to, a single 

 muscle-bud. It may be asserted with confidence that a radial 

 muscle is derived, at least mainly, from that bud 

 Avhose position it later occupies; and that the radial 

 muscles in the normally developed region of the 

 paired fin of an Elasmobranch corresponds accu- 

 rately in number and position to the group of primi- 

 tive buds from which they have been formed.^ 



There is a last objection which Brans persistently reiterates 

 in his papers, and of which he makes a great deal. He alleges 

 that the " concordance " which exists in the adult between the 

 radial muscles and the radial cartilages is not primitive, but 

 secondary. He states that in the early stages of development 

 there are " discrepancies " between these elements, that the 

 muscle-buds do not correspond exactly with the rudiments of 

 the radials, and that the perfect correspondence, or concord- 

 auce, is gradually established in later stages. This subject 

 will be dealt with later on in greater detail (p. 357) ; but it 

 may here be said that the evidence on which Brans bases his 

 aro-ument seems to be of the slenderest and most unconvincing 

 nature. Not even in the adult is the concordance perfect; 

 marked disturbances occur at both the anterior and the pos- 

 terior extremities of the fins. The peripheral ends of the adult 

 muscles correspond exactly with the radials in the middle 



1 If it is objected that in Ceratodus, where the adult paired fin lias about 

 thirty radials and radial muscles, only about three segments have been shown 

 to contribute muscle-buds in the embryo (Semon 33), it must be answered 

 that this result is not trustworthy. Davidoff (8) and Braus (3) have found 

 twelve spinal nerves contributing to the limb-plexus. It is probable that 

 llabl's formula holds good iu Ceratodus (MoUier 24), and that a large and 

 sufficient number of segments really contribute muscle-forniing cells to the 

 limb, but not in the form of distinct buds. 



