246 EMBRYOLOGY. 



human embryo has nothing to do with the development of the 

 belly -stalk. 



Neither of these two explanations seems to me entirely satisfactory. 

 According to my view, the structure under consideration may be 

 explained in a manner which is not only in complete harmony with 

 the facts of the case, but also reconciles the views of KOLLIKER and 

 His. 



As COSTE'S embryo appears to show, the origin of the belly-stalk is 

 connected in the first place with a somewhat irregular formation of the 

 amnion. It follows from the fact that the latter is drawn out 

 posteriorly to a point (fig. 141 am 1 ), the apex of which reaches to the 

 chorion, that its closure in the human embryo takes place at the 

 extreme posterior end of the body, and that at the same time a union 

 with the chorion is retained at the place of closure. The fundament 

 of the embryo therefore remains in connection with the chorion, not 

 directly, as His maintains, but only indirectly by means of tlie 

 amnion. 



In the second place, the allantois, the somewhat eccentric develop- 

 ment of which in the case of Man is perhaps intimately connected 

 with the above-mentioned peculiarity in the formation of the amnion, 

 takes part in the formation of the belly-stalk. It is therefore proper 

 in this connection to enter somewhat more fully into the allantois- 

 question in Man, so actively discussed during the last decade. 



Since in other Mammals the allantois (fig. 142 al) has the form of 

 a large stalked sac, which grows out from the navel till it comes in 

 contact with the serosa (sz), and carries to it, along with connective 

 tissue, the umbilical vessels, attempts have been made ever and anon 

 to discover such a structure in the case of human embryos also. The 

 proof of its existence in Man appeared to be furnished by a premature 

 embryo, on which KRAUSE described a spherical, sac-like allantois. 



The embryo of KRAUSE presented, however, in many respects 

 such deviations from other known human embryos of the corre- 

 sponding stage as to cause the statements to be accepted on the part of 

 many persons with great reservation, and to permit the suggestion 

 of His, that in this case it was not after all a human embryo. 



Upon critical examination of the facts relating to the question, 

 I am likewise of the opinion that in the case of Man a stage of 

 development with a free allantoic sac protruding out of the body-cavity 

 is not reached. 



As results from the fine investigations of human embryos by His, 

 the belly-stalk is found upon cross section to be composed of : 



