IOO METAMORPHOSIS. 



oesophagus of the adult, and joins the primitive oral cavity at 

 the velum. The so-called bronchus of the adult is thus the 

 whole branchial region of the Ammoccetes, and the anterior 

 part of the oesophagus of the adult is an entirely new forma- 

 tion. 



3. The posterior part of the alimentary tract of the Ammo- 

 ccetes undergoes partial atrophy. The gall-bladder of the liver 

 is absorbed ; and the liver itself ceases to communicate with the 

 intestine. 



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 1 , 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. in. 1877. 



(79) C. Kupffer u. B. Benecke. Der Vorgang d. Befruchtiing am Ei d. 

 Neunaugen. Konigsberg, 1878. 



(80) Aug. Miiller. " Ueber die Entwicklung d. Neunaugen." Muller's 

 Archiv, 1856. 



(81) Aug. Miiller. Beobachtungen iib. d. Befruchtungserscheinungcn itn Ei d. 

 Neunaugen. Konigsberg, 1864. 



J Cyclopadia of Aitat. and Tliys. Article 'Ovum.' 



