mi: i .1.1 \i. MI 





a 



sole-like form; meanwhile it gTOWl to ;i length : 3'5 mm. 



(li-. 131). 



As baa been already described in bfa previous chapter, at this 

 time the middle germ-layer spreads out in tin- embryonic- t'mulainent, 

 the medullary groove (ligs. l.'Jn and 131 ?/), the chorda, and a 

 number of primitive segments are forum I, 

 and, on the eight li day, the first trace of 

 the vessels and blood appears in tip 

 riilar a i-i -a (<). On the ninth and tenth 

 days the embryonic fundament is by a 

 pn>ces> of fob ling converted into the body 

 of the embryo, and is constricted off from 

 the remaining part of the blastodermic 

 \e-icle, out of which at the same time 

 various f.etal membranes begin to be de- 

 veloped. The initial stages of all 

 processes are the same in Mammals as in 

 Birds and Eeptiles, so that we can e.\ 

 on i>elves very briefly in describing them. 

 \Ve -hall connect the description with the 

 diagrammatic drawings which KOLLIKER 

 has made, ai.d which have found a place 

 in many text-books (fig. 132, 1-5). 



Diagram 1 shows a blastodermic vesicle 

 which in the Rabbit would correspond to 

 about the seventh or eighth day. It is 

 still enclosed from without by the very 

 much attenuated vitelline membrane (d), 

 which is now also called prochorion. 

 in many Mammals flakes and slnv.U of 

 albumen have been precipitated on its 

 outer surface out of the fluid secreted by 

 the mucous membrane of the uterus. The 

 inner germ-layer (i) which in a slightly 



younger blastula, such as is represented in tigmv iches only 



to the line ge, and still leaves uncovered a third of the inner surface 

 of the sphere has now entirely grown around to the vegetati\e j ole. 

 The middle germ-layer ( //* ) is in full process of development, and 

 embraces about a fourth part of the surface of the sphere. A small 

 portion of this three- layered region contain.- the embryonic funda: 

 which would be in about that stage of development which we have 



15 



fig. 131. Embryonic fundair.fr t 

 of a Rabbit of nine days with 

 a portion of the area pellucida, 

 fiviu K'.'.i i D 



.-/;*. Are;ii-i !l U'-ul.i :rto,areaopaca ; 

 h', h", //", nirtlull.uy plate in 

 X\on of the first, second, 

 ami third ceivbr.il vou-les ; stz, 

 stem-zone (Stamrnxon-) 

 I.HI it tal zone ; r/, dorsal f r 



