4. The eye undergoes important changes in that it travels to the surface, and acquires all the characters of the normal vertebrate eye.
5. The brain becomes relatively larger but more compact, and the optic lobes (corpora bigemina) become more distinct.
6. The pericardial cavity becomes completely separated from the body cavity, and a distinct pericardium is formed.
7. The mesonephros of the larva disappears, and a fresh posterior part is formed.
Myxine. The ovum of Myxine when ready to be laid is inclosed, as shewn by Allen Thomson[32], in an oval horny shell in many respects similar to that of Elasmobranchii; from its ends there project a number of trumpet-shaped tubular processes, which no doubt serve to attach it to marine objects. No observations have been made on the development.
Bibliography.
(77) E. Calberla. “Der Befruchtungsvorgang beim Petromyzon Planeri.” Zeit. f. wiss. Zool., Vol. XXX. 1877.
(78) E. Calberla. “Ueb. d. Entwicklung d. Medullarrohres u. d. Chorda dorsalis d. Teleostier u. d. Petromyzonten.” Morpholog. Jahrbuch, Vol. III. 1877.
(79) C. Kupffer u. B. Benecke. Der Vorgang d. Befruchtung am Ei d. Neunaugen. Königsberg, 1878.
(80) Aug. Müller. “Ueber die Entwicklung d. Neunaugen.” Müller’s Archiv, 1856.
(81) Aug. Müller. Beobachtungen üb. d. Befruchtungserscheinungen im Ei d. Neunaugen. Königsberg, 1864.
(82) W. Müller. “Das Urogenitalsystem d. Amphioxus u. d. Cyclostomen.” Jenaische Zeitschrift, Vol. IX. 1875.
(83) Ph. Owsjannikoff. “Die Entwick. von d. Flussneunaugen.” Vorläuf. Mittheilung. Mélanges Biologiques tirés du Bulletin de l'Acad. Imp. St Pétersbourg, Vol. VII. 1870.
(84) Ph. Owsjannikoff. On the development of Petromyzon fluviatilis (Russian).
(85) Anton Schneider. Beiträge z. vergleich. Anat. u. Entwick. d. Wirbelthiere. Quarto. Berlin, 1879.
(86) M. S. Schultze. “Die Entwickl. v. Petromyzon Planeri.” Gekrönte Preisschrift. Haarlem, 1856.
(87) W. B. Scott. “Vorläufige Mittheilung üb. d. Entwicklungsgeschichte d. Petromyzonten.” Zoologischer Anzeiger, Nos. 63 and 64. III. Jahrg. 1880.
[23] The following classification of the Cyclostomata is employed in the present chapter:
I. Hyperoartia ex. Petromyzon.
II. Hyperotreta ex. Myxine, Bdellostoma.
[24] The present chapter is in the main founded upon observations which I was able to make in the spring of 1880 upon the development of Petromyzon Planeri. Mr Scott very kindly looked over my proof-sheets and made a number of valuable suggestions, and also sent me an early copy of his preliminary note (No. [87]), which I have been able to make use of in correcting my proof-sheets.
[25] Der Ursprung d. Wirbelthiere, etc. Leipzig, 1875.