372 EDWIN S. GOODRICH. 



probably no real motor plexus^ but tlie motor nerves may be 

 gathered together into more or less longitudinal collectors^ 

 and become again sorted out on reaching the musculature. 

 Such collectors are found at the base of the dorsal fins, com- 

 pounded of some fourteen to sixteen segmental rami pterygiales. 

 All the fins remain throughout development in approximately 

 the same position. Apparent change of place may be brought 

 about by concentration being greater in the one direction 

 than in the other. This is especially the case with the dorsal 

 fins, the anterior edge of which may undergo a relative shift- 

 ing over some ten segments. 



The general bearing of these results has been sufficiently 

 discussed in the Introduction (p. 334), and need not again be 

 dealt with here. But it may be pointed out how completely 

 they support the lateral fold theory of the origin of the paired 

 fins. 



List of References. 



1 . Balfoub, F. M. — " A Monograph on the Development of ElasmobraucL 



Fislies," ' Journ. of Anat. and Fliys./ 1876-8. 



2. Balfour, F. M. — "On tlie Development of the Skeleton of the Paired 



Fins of Elasmobranchii," ' Proc. Zool. Soc. London,' 1881. 



3. Bkaus, [i. — " Ueber die Innervation der Paarigen Extremitaleu bei 



Selachiern," 'Jen. Zeitschr. fiir Naturw.,' Bd. xxix, 1895. 



4. Bkaus, H. — "Beitriige zur Entwickl. d. Muskuhitur u. d. periph, Nerven- 



system d. Selachier," 'Morph. Jahrb.,' Bd. xxvii, 1899. 



5. BiiAUS, H. — "Thatsachlichesaus der Entwickl. d. Extremitatenskeletles," 



'Haeckelfestschrift Deukschr. Med. -Nat. Ges.,' Jena, 1901. 



6. Bkaus, H. — " Die Muskein u. Nerven der Ceratodusflosse," ' Zool. 



Forsch. Denkschr. Med. -Nat. Ges.,' Jena, 1901. 



7. Bkaus, H. — " Die Entwickl. d. Form. d. Extremitsiten u. d. Extremi- 



Ijiteuskeletts," ' Hertwig's Haiidbucii d. vergl. u. exp. Eiilwick. 

 der Wirbelticre,' 1901. 



8. Davidoff, v. M. — "Beitriige z. vergl. Anatomie der hintercn Gliedmasse 



der Fische," ' Morph. Jahrb.,' Bd. v, 1879. 



9. Dkan, B. — " Historical Evidence as to the Origin of the Paired Limbs 



of Vertebrates," * Am. Nat.,' v. xx.wi, 1902. 



