STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 793 



In support of this statement we may point: (i) To the 

 structure of the sheath of the notochord ; (2) to the formation of 

 the greater part of the bodies of the vertebrae from ossification 

 in membrane around the notochord ; (3) to the early biconcave 

 form of the vertebras, only masked at a later period by the de- 

 velopment of intervertebral cartilages ; (4) to the character of 

 the neural arches. 



This latter feature will be made very clear if the reader will 

 compare our figures of the sections of later vertebrae (Plate 42, 

 fig. 78) with Gotte's 1 figure of the section of the vertebra of a 

 Pike (Plate 7, fig. i). In Gotte's figure there are shewn similar 

 intercalated pieces of cartilage to those which we have found, 

 and similar cartilaginous dorsal processes of the vertebras. Thus 

 we are justified in holding that whether or no the opisthoccelous 

 form of the vertebrae of Lepidostens. is a commencement of a 

 type of vertebrae inherited by the higher forms, yet in any case 

 the vertebrae are essentially built on the type which has become 

 inherited by the Teleostei from the bony Ganoids. 



PART III. The ribs of Fishes. 



The nature and homologies of the ribs of Fishes have long 

 been a matter of controversy ; but the subject has recently been 

 brought forward in the important memoirs of Gotte 2 on the 

 Vertebrate skeleton. The alternatives usually adopted are, 

 roughly speaking, these : Either the haemal arches of the tail 

 are homologous throughout the piscine series, while the ribs 

 of Ganoids and Teleostei are not homologous with those of 

 Elasmobranchii ; or the ribs are homologous in all the piscine 

 groups, and the haemal arches in the tail are differently formed 

 in the different types. Gotte has brought forward a great body 

 of evidence in favour of the first view; while Gegenbaur 3 may 



1 "Beitrage zur vergl. Morphol. d. Skeletsystems d. Wirbelthiere." Archiv f. 

 Mikr. Anat. Vol. xvi. 1879. 



2 " Beitrage z. vergl. Morph. d. Skeletsystems d. Wirbelthiere. II. Die Wir- 

 belsaule u. ihre Anhange." Archvo /. Mikr. Anat., Vol. xv., 1878, and Vol. xvi., 

 1879. 



3 " Ueb. d. Entwick. d. Wirbelsaule d. Lepidosteus, mit. vergl. Anat. Bemer- 

 kungen. "Jena ische Zeitschrift, Bd. in., 1863. 



B. 51 



