66 BIBLIOGRAPHY. 



the liver by the venous trunk from the yolk-sack. The venous 

 trunk leaves the body on the right side, and the arterial on the 

 left. 



The yolk-sack persists during the whole of embryonic life, 

 and in the majority of Elasmobranch embryos there arises 

 within the body walls an outgrowth from the umbilical canal 

 into which a large amount of the yolk passes. This outgrowth 

 forms an internal yolk-sack. In Mustelus vulgaris the internal 

 yolk-sack is very small, and in Mustelus laevis it is absent. 

 The latter species, which is one of those in which development 

 takes place within the uterus, presents a remarkable peculiarity 

 in that the vascular surface of the yolk-sack becomes raised into 

 a number of folds, which fit into corresponding depressions in 

 the vascular walls of the uterus. The yolk-sack becomes in this 

 way firmly attached to the walls of the uterus, and the two 

 together constitute a kind of placenta. A similar placenta is 

 found in Carcharias. 



After the embryo is hatched or born, as the case may be, the 

 yolk-sack becomes rapidly absorbed. 



BIBLIOGRAPHY. 



(40) F. M. Balfour. " A preliminary account of the development of the Elasmo- 

 branch Fishes." Quart. J. of Micr. Science, Vol. xiv. 1876. 



(41) F. M. Balfour. "A Monograph on the development of Elasmobranch 

 Fishes." London, 1878. Reprinted from the Journal of Anat. and Physiol. for 1876, 

 1877, and 1878. 



(42) Z. Gerbe. " Recherches sur la segmentation de la cicatrule et la formation 

 des prodnits adventifs de Fceuf des Plagiostomes et particulierement des J?aies." Vide 

 also Journal de F Anatomic et de la Physiologic, 1872. 



(43) W. His. " Ueb. d. Bildung v. Haifischenembryonen." Zeit, filr Anat. u. 

 Entrvick., Vol. n. 1877. 



(44) A. Kowalevsky. "Development of Acanthias vulgaris and Mustelus 

 Isevis. " (Russian.) Transactions of the Jfiew Society of Naturalists, Vol. I. 1870. 



(45) R. Leuckart. " Ueber die allmahlige Bildung d. Korpergestalt bei d. 

 Rochen." Zeit. f. iviss. Zool., Bd. n., p. 258. 



(46) Fr. Leydig. Rochen n. Haie. Leipzig, 1852. 



(47) A. W. Malm. " Bidrag till kannedom om utvecklingen af Rajas." Kongl. 

 vetenskaps akademiens fdrhandlingar. Stockholm, 1876. 



(48) Joh. Miiller. Clatter Haie des Aristoteles und ilber die Verschiedenhriten 

 untcr den Haifischen und Rochen in der Entwicklung des Eies. Berlin, 1840. 



(49) S. L. Schenk. " Die Eier von Raja quadrimaculata innerhalb der Eileiter." 

 Sitz. der k. Akad. IVien, Vol. LXXIII. 1873. 



