Embryonic Development in Man. 377 



In the latter at some distance from the ovum an inner spongiosa 

 and an outer compada can generally be easily distinguished. The 

 mesoderm lining the interior of the chorionic cavity or exocoelom 

 will be designated as the chorion mesoderm, while the chorion ecto- 

 derm will be called trophohlast. This term has been proposed by 

 Hubrecht, and it is understood and used so generally that it is 

 perhaps well to retain and not to replace it by other terms.^ The 

 trophoblast is composed of two kinds of tissue, the inner cell masses 

 and an outer covering of syncytium. We want to state here that 

 the examination of our young ovum has confirmed our opinion, 

 expressed a number of times previously, that both the cells proper 

 of the trophoblast (the future Langhans cell layer) and the syncy- 

 tium are derived from the fetal ectoderm. We have never pre- 

 viously in hundreds of placentas in normal and in ectopic gestation, 

 nor in our present case, found anything which would seriously sug- 

 gest a derivation of the trophoblast syncytium from maternal cells. 

 The ovum under discussion nowhere shows a possibility that the 

 syncytium is derived either from surface or glandular uterine epithe- 

 lium, from vascular endothelium, or from decidual cells. Hence the 

 term edohlast shell for the combined trophoblast cells and the syncy- 

 tium is correct. We retain the well-known term trophoblast in 

 spite of the fact that we consider it as to its etymology a misnomer. 

 We have previously expressed ourselves on this subject, as follows : 



^'The term trophoblast has been given by Hubrecht to the extra- 

 embryonic ectoblast shell under the impression that it had to do a good 

 deal with the nutrition of the early embryo. We doubt, however, that 



"Miiiot, in an address ou "The Implantation of the Human Ovum in the 

 Uterus," delivered in 1904 before the Gynecological Society and printed in its 

 transactions, has proposed the term trophoderm, hut he states himself: "In 

 the address the term trophoblast was used in accordance with my under- 

 standing of Professor Hubrecht's views and consent; but, as Professor Hu- 

 brecht has objected to this application of his term, it has been necessary to 

 propose a new one. I regret that so good a name as trophoblast has to be 

 dropped." With this address the author only became familiar after the 

 completion of the manuscript of this contribution. He now finds that his 

 views of the physiology and the mechanism of the implantation of the 

 human ovum given are in many respects identical with the previously pub- 

 lished explanations of Minot. 



