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SUMMARY OF CURRENT RESEARCHES RELATING TO 
months of the maternal crypts, with the result that the maternal epithe- 
lium is destroyed wherever the trophoblast adheres ; it then undergoes a 
differentiation into an outer layer which assumes the syncytial character 
more fully and contains paler nuclei, and an inner layer, the nuclei of 
which stain more strongly. Internuclear spaces are developed in the 
plasmodioblast. and enter into communication with the maternal spaces 
that have been laid bare after the disappearance of the maternal epithe- 
lium. The trophoblastic protuberances that have penetrated into 
the crypts are hollowed out, and allantoidean villi enter into these 
cavities. Later on, newly formed villi are enclosed by a trophoblastic 
matrix identical with that around their earliest predecessors. As the 
placentary region increases in breadth, space is gained for the free de- 
velopment of these secondary villi ; at the same time the maternal pro- 
liferation flattens out and becomes a covering for the growing placenta, 
and is finally reduced to isolated nuclear remnants. In the final stage 
of the placenta the allantoidean villi are no longer recognizable as such, 
and the intervening trophoblast is stretched to the utmost ; the thinnest 
layer of plasmodioblast tissue is then the only separation between the 
maternal and the embryonic blood-fluids. 
Prof. Hubreeht thinks it is clear that the placenta is essentially an 
embryonic neo-formation which is permeated by maternal blood that 
circulates in spaces devoid of endothelium. This embryonic neomorph is 
preceded by a considerable proliferation of maternal epithelium, which 
does not enter into the constitution of the ripe placenta, but affords 
facilities of fixation and nutrition for the new formation in its earliest 
stages. 
Development of Mullerian Duct in Mammals.* — Dr. M. J. van Erp 
Taalman Kip first examined the development of this duct in various 
Insectivora, Tupaia , Talpa , Erinaceus, and Sorex. Of these the first is 
the easiest to understand ; in it the Mullerian duct consists of two parts 
which are genetically quite distinct ; the ostium and the part of the 
duct nearest it arise from the peritoneal epithelium, while the remainder 
of the duct is largely derived from the Wolffian duct. The number of 
infundibular orifices laid down to form the permanent ostium varies 
somewhat ; generally three are laid down, of which two are further 
developed. Much the same conditions obtain in Talpa. In Erinaceus 
the part derived from the peritoneal epithelium is shorter than its 
homologue in the two preceding genera. 
These observations appear to the author to afford a simple explana- 
tion of the difference between Selachians and Urodeles, where the Mul- 
lerian duct arises from the archinephric duct, and Reptiles, where it is in- 
dependent of it. The difference between the upper and lower parts of 
the duct is widely diffused among Vertebrates ; in Selachians it becomes 
independent from behind forwards, while the complete independence 
seen in Reptiles, many Birds, and perhaps, also, many Mammals, is ceno- 
genetic. Animals closely related to one another may show great differ- 
ences, and as the same is true of varieties of one and the same species, 
we can understand why observers have obtained contradictory results. 
* Tijdschr. Nederl. Dierk. Vereen., iv. (1894) pp. 71-174 (Dutch), pp. 175-84 
(German resume), 3 pis. 
