STUDIES m MAMMALIAN EMBIIYOLOGY. 483 



mental phenomena has been noticed in my preparations 

 which would require a similar explanation, we may safely 

 conclude that either the phenomena of placentation are iden- 

 tical in Sorex vulgaris and Sorex fodiens, or that no 

 uteri of the latter species are among those that have been 

 investigated and figured by me. 



In the illustrations of this paper I have endeavoured to give 

 the drawings on each plate, as far as possible, on scales of 

 enlargement that will allow of a more direct comparison of 

 the different figures among themselves. In figs. 1 to 16 the 

 general outlines (drawn with the camera) of the process of 

 placentation in the shrew are diagrammatically delineated. The 

 maternal tissues are there represented by red, the embryonic 

 tissues by black lines. The red numbers indicate the catalogue 

 number of the specimens ; the small numbers (red or black) 

 have reference to the number of the figure in which the region 

 thus indicated is drawn with more histological detail under 

 higher power. 



Leaving the histological questions to be fully discussed 

 further on, I will first, by the aid of these figs. 1 to 15, give a 

 general and succinct description of the principal facts that 

 present themselves concerning the growth of the shrew's 

 blastocyst, and its more intimate connection with the mater- 

 nal tissues and the maternal circulation. 



All these figures have been drawn with the camera from the 

 actual preparations with Zeiss's apochromatic obj. 16 mm., 

 oc. 1, tub. 160, distance between ocular and paper 24 cm. 

 They are thus strictly comparable also in regard to size. 



To this paper no chapter is added in which the points of 

 agreement and of difference between the results here obtained 

 and those to which recent investigators (Duval, Strahl, Fieisch- 

 mann, Marius, Minot, Heinricius, Liisebrink, &c.) have 

 arrived with respect to other species of Mammalia, are dis- 

 cussed. 



Nor are any general and comparative considerations with 

 respect to the theory of placentation here advanced. This 

 was done on purpose, because the material is already at hand 



