PAIKED FINS WITH THEIR NERVES, IN LEPIDOSIREN AND PROTOPTERUS. 63T 



The separation of the hypoglossal and pectoral limb musculature, and hence of 

 their nerve plexuses, is brought about by the relation of the pronephros to the ventral 

 processes of the myotomes concerned. 



The pectoral fin affords clear evidence that it has lately undergone a forward migra- 

 tion, and that posterior myotomes are successively ceasing to take part in it. True 

 muscle buds are not formed, the cells being given off from the walls of the ventral 

 processes. 



The pelvic fin appears later than the pectoral. There is no sign of a continuous 

 pectoral and pelvic fin rudiment. Apparently eight myotomes take part in its 

 muscular isation, which agrees with the composition of the pelvic plexus. The pelvic 

 limb gives evidence of a former backward migration of the same nature as that for the 

 forward migration of the pectoral fin, together with additional evidence from the con- 

 dition of the ectodermal rudiment. It has migrated backwards till stopped by the 

 cloaca, the variations in the position of which it closely follows. A comparison of the 

 two genera leads to the conclusion that these variations in the position of the cloaca 

 are due to variations in the total number of segments in the body. 



LIST OF PAPERS REFERRED TO. 



(1) Agar, W. E., " The Development of the Skull and Visceral Arches in Lepidosiren and Protopterus," 



Trans. Roy. Soc. Edin., vol. xlv., 1906. 



(2) Balfour, F. M., A Treatise on Comparative Embryology, London, 1880. 



(3) Braus, H., " Uber die Innervation der paarigen Extremitaten bei Selachiern, Holocephalen und 



Dipnoern," Jen. Zeitsrhr., xxxi., 1898. 



(4) " Beitrage zur Entwickelung der Muskulatur und des peripheren Nervensystems der Selachier," 



Morpli. Jahrb., xxvii., 1899. 



(5) Broman, I., " Ueber die Entwickelung des Mesenterien, der Leberligamente und der Leberform bei den 



Lungenfischen," Semon's Zoolog. Forschungsreisen, V. Lief., 1905. 



(6) Corning, H. K., " Uber einige Entwicklungsvorgange am Kopfe der Anuren," Morph. Jahrb., xxvii., 



1899. 



(7) "Uber die Entwicklung d. Kopf- und Extremitaten-Muskulatur bei Reptilien," Morph. Jahrb., 



xxviii., 1899. 



(8) Dohrn, A., " Studien zur Urgeschichte des Wirbelthierkorpers : XV. (Metamerie des Kopfes)," Mitih. 



a.i/. Zool. Station zu Neapel, ix., 1890. 



(9) Froriep, A., "Entwick. des Kopfes," Merkel und Bonnet's Ergebnisse, i., 1891. 



(10) "Zur Entwicklungsgeschichte des YVirbeltierkopfes," Verh. d. Anat. Gesellsch., 1902. 



(11) Furbringer, M., "Ueber die spino-occipitalen Nerven der Selachier und Holocephalen und ihre 



vergleichende Morphologie," Festsch. fur Gegenbaur, Bd. iii., 1897. 



(12) Gegenbaur, C, "Die Metamerie des Kopfes und die Wirbeltheorie des Kopfskeletes," Morph. Jahrb., 



xiii., 1887. 

 Vergleichende Anatomie d. Wirbelthiere, Leipzig, 1898. 



(13) Gregory, E. H, "Die Entwick. der Kopfhbhlen und des Kopfmesoderms bei Ceratodus forsteri," 



Semon's Zoolog. Forschungsreisen, V. Lief., 1905. 



(14) Harrison, R. G., "The Growth and Regeneration of the Tail of the Frog Larva," Archiv fur Ent- 



wickelung smech, vii., 1896. 



