The following account is given by Rathke (No. 72*) and Lereboullet (No. 71). At first a subintestinal vein (_vide_ chapter on Circulation) falls into the lacunæ of the yolk-sack, and the blood from these is brought back direct to the heart. At a later period, when the liver is developed, the subintestinal vessel breaks up into capillaries in the liver, thence passes into the yolk-sack, and from this to the heart. An artery arising from the aorta penetrates the liver, and there breaks up into capillaries continuous with those of the yolk-sack. This vessel is perhaps the equivalent of the artery which supplies the yolk-sack in Elasmobranchii, but it seems possible that there is some error in the above description. BIBLIOGRAPHY. (55) Al. Agassiz. "On the young Stages of some Osseous Fishes. I. Development of the Tail." _Proceedings of the American Academy of Arts and Sciences_, Vol. XIII. Presented Oct. 11, 1877. (56) Al. Agassiz. "II. Development of the Flounders." _Proceedings of the American Acad. of Arts and Sciences_, Vol. XIV. Presented June, 1878. (57) K. E. v. Baer. _Untersuchungen über die Entwicklungsgeschichte der Fische._ Leipzig, 1835. (58) Ch. van Bambeke. "Premiers effets de la fécondation sur les oeufs de Poissons: sur l'origine et la signification du feuillet muqueux ou glandulaire chez les Poissons Osseux." _Comptes Rendus des Séances de l'Académie des Sciences_, Tome LXXIV. 1872. (59) Ch. van Bambeke. "Recherches sur l'Embryologie des Poissons Osseux." _Mém. couronnés et Mém. de savants étrangers de l'Académie roy. Belgique_, Vol. XL. 1875. (60) E. v. Beneden. "A contribution to the history of the Embryonic development of the Teleosteans." _Quart. J. of Micr. Sci._, Vol. XVIII. 1878. (61) E. Calberla. "Zur Entwicklung des Medullarrohres u. d. Chorda dorsalis d. Teleostier u. d. Petromyzonten." _Morphologisches Jahrbuch_, Vol. III. 1877. (62) A. Götte. "Beiträge zur Entwicklungsgeschichte der Wirbelthiere." _Archiv f. mikr. Anat._, Vol. IX. 1873. (63) A. Götte. "Ueber d. Entwicklung d. Central-Nervensystems der Teleostier." _Archiv f. mikr. Anat._, Vol. XV. 1878. (64) A. Götte. "Entwick. d. Teleostierkeime." _Zoologischer Anzeiger_, No. 3. 1878. (65) W. His. "Untersuchungen über die Entwicklung von Knochenfischen, etc." _Zeit. f. Anat. u. Entwicklungsgeschichte_, Vol. I. 1876. (66) W. His. "Untersuchungen über die Bildung des Knochenfischembryo (Salmen)." _Archiv f. Anat. u. Physiol._, 1878. (67) E. Klein. "Observations on the early Development of the Common Trout." _Quart. J. of Micr. Science_, Vol. XVI. 1876. (68) C. Kupffer. "Beobachtungen über die Entwicklung der Knochenfische." _Archiv f. mikr. Anat._, Bd. IV. 1868. (69) C. Kupffer. _Ueber Laichen u. Entwicklung des Ostsee-Herings._ Berlin, 1878. (70) M. Lereboullet. "Recherches sur le développement du brochet de la perche et de l'écrevisse." _Annales des Sciences Nat._, Vol. I., Series IV. 1854.