Nachdruck verboten, 

 üebersetzungarecht vorbehalten. 



The Birth-period of Trichosums vulpecula. 



By 



J. Beard, D. Sc, 



University Lecturer in Comparative Embryology and in Vertebrate 

 Morphology, Edinburgh. 



With Plate 6. 



A year ago, in a memoir^) dealing with and establishing the 

 existence of a corresponding phase in the development of various 

 Vertebrates from fishes, such as Scylliwm and Baja., to mammals, such 

 as the rabbit, pig, and man, it fell to me to examine, and fix by 

 comparison, the period at which a marsupial, Didelphys virginiana, 

 is born. 



It is well-known, that we are indebted to the classic memoirs 2) 

 of Selenka for an account of the embryonic history of this form 

 until its birth, and it was from an examination and tabulation of his 

 finds concerning the degree of development of the new-born opossum, 

 that I was able to show, that the animal enters the world at a period 

 of its life, when its degree of development is about the equivalent 

 of that of a Scyllium-embryo, which is just taking, or about to take, 

 yolk into its gut, of that of a rabbit-embryo, which is just commencing 

 to use its allantoic placenta, of that of a pig-embryo, corresponding 

 to Keibel's ^) fig. 68, or of that of a human embryo of some 45—47 



1) Beard , J., On Certain Problems of Vertebrate Embryology. 

 Jena, Gustav Fischer, 1896. 



2) Selenka, E., Studien zur Entwickl. der Tbiere, Hft. 4 u. 5. 



3) Keibbl, f., Studien zur Entwicklung des Schweines , TI, in : 

 Morph. Arbeiten, V. 5, pp. 17 — 168, 7 plates. 



