418 THE PHYSIOLOGY OF REPRODUCTION 



the ectoderm and entoderm, whence it is transmitted to the cavity 

 oi' the yolk-sac and serves for nutriment (Hill 1 ). The gestation 

 JM -i.id is alx)iit eight days, as in the opossum. 



In rn-rtini'li-it the placental structures are better developed (Hill 2 ). 

 Before the attachment of the blastocyst, the uterine mucosa under- 

 goes preliminary changes. The capillaries increase in size and new 

 vessels are formed ; the interglandular tissue is composed of a loose 

 network of anastomosing cells and the inter-spaces are filled with 



FIG. 104. Diagram showing the arrangement of the foetal membranes in Dani/in-im. 

 (From Hill, " On the Fietal Membranes, Placentation, and Parturition of 

 the Native Cat (DatjfttfUt mverriitiix)" A/ixt. Anzeig., vol. xviii., 1900. 



"//.//, Trunk amnion ; fill, allantois ; Iril.omph, bilaminar omphalopleur ; ch, 

 chorion (diplo-trophoblast) ; roe, extra-embryonic splanchnocele ; proa, 

 proamnion ; proa.l, posterior limit of proamnion ; s.t, sinus terminals ; 

 vasc.mnph, vascular omphalopleur ; y.<-, cavity of yolk-sac ; y., yolk-stalk ; 

 y.npl, invaginated yolk-sac splanchnopleur : the ectoderm is represented by a 

 thm line, the entoderm by a dotted line, and the mesoderm by a thick line. 



lymph, the glands increase in length and diameter, and the cells of 

 the surface epithelium lose their boundaries, and fuse to form a 

 >\ iicytium analogous to the nyjuji/nxiiKt of higher forms (see p. 445). 



Opposite the coelom, the blastocyst becomes attached to a discoidal 

 area of the uterine symplasma by means of enlarged ectodermal cells, 

 and later its wall is vascularisei 1 by the allantois. Outside the disc, 

 the part corresponding to the area vasculosa is also attached by an 

 annular /one. and ;i yolk-sac placenta is formed. The non-vascular 



1 Hill, "On the rVtal Membranes, etc., of the Native Cat (Dagyurus vwer- 

 /////)," Aunt. Anz., vol. xviii., 1900. 



- Hill, "The Placentation of /'<,,/,//</,>.*," (fnar. Jnnr. Micr. >'/,/"/, vol. xl., 

 1898. 



