484 HENRY F. OSBORN. 



nutriment from the uterus through the contiguous umbilical 

 vessels, the allantois retaining solely its reptilian functions. 



(2.) With the diminution of food yolk came an increasing 

 absorption of maternal nutriment through the chorion of the 

 yolk-sac, upon which villi gradually appeared. The Marsu- 

 pials may fall into this or the following class. 



(3.) A condition in which the allantois and yolk-sac shared 

 the placental function. 



(4.) The primitive Placentalia (Balfour), in which the yolk- 

 sac formed a large false chorion, and the allantois formed a 

 small discoid placenta, and in which the maternal parts were 

 not deciduous. 



I hope during the spring of 1884 to be able to follow out 

 the membranes of the opossum to the later stages. At present, 

 owing to the hurried preparation of this paper, some valuable 

 drawings have been omitted, and the study of the kangaroo 

 was not so complete as I desired, nor have I been able to refer 

 to all the authorities upon the subject, as I hope to do in a 

 later paper. 



Ma^ \m, 1883. 



