524 A. A. W. HUBRECHT. 



EXPLANATION OF PLATES 31 to 39, 



Illustrating Professor A. A. W. Hubrecht's paper " Studies 

 in Mammalian Embryology. III. — The Placentation of 

 the Shrew (Sorex vulgaris)/" 



List of Abbreviations, 

 a. T. Allantoidean trophoblast. o. T. Omphaloidean trophoblast. tr. an. 

 Trophoblastic annulus. an! . Embryonic cells which grow downwards from 

 the upper rim of the trophoblastic annulus and adhere against the maternal 

 tissue, np. T. Non-placental trophoblast. k. Trophoblastic knobs which 

 become hollowed out and into which allantoidean villi penetrate. U. Lumen 

 of the uterus, u. E. Uterine epithelium, gl. Uterine glands. M. Meso- 

 metrium. ep. Epithelial crypts in the proliferating portion of the maternal 

 mucosa. S. Strands of epithelial tissue between the superficial and deeper 

 maternal layers in the omphaloidean region, bl. Blood-vessels. Im. Longi- 

 tudinal, and cm. Circular fibres of the muscularis. y. Yolk-sac. a. v. Area 

 vasculosa. E. c. Extra-embryonic coeloma. am. Amnion, pr. am. Proamnion, 

 all. Allantois. vi. Allantoidean villus, g. c. Green coagulum in the yolk- 

 sac, mes. Mesoblast. s. m. Somatic mesoblast. hy. Hypoblast. 7m. Nuclear 

 nests in the syncytium (incipient blood-spaces). 



PLATES 31 and 32. 

 Outline sketches of median transverse sections through uterus and embryo 

 in successive stages of pregnancy of Sorex vulgaris. All tlie figures 

 drawn with the camera. X 27. Embryonic tissue in black, maternal 

 tissue in red outlines. The red numbers in brackets refer to the catalogue 

 number of the specimen. The small numerals connected with dotted lines 

 refer to figure-numbers on the subsequent plates in which the region thus 

 indicated is represented as seen under stronger powers. Cf, Eigs. 36 — 47 

 for the outward aspect of the uterus in the stages from that of figs. 8 — 15. 



Figs. 1 and 2. — The blastocyst has not yet arrived in the cavity of the 

 uterus, but is still contained in the oviduct. 



Fig. 1.— Utr. Mus. Cat. n°- Sorex 124/, 3 r. 4 s. 

 Fio'. 2.— „ „ 110 2, 2 r. 16 s. 



EiGS. 3 and 4.— Sudden and peculiar extension of the uterus lumen and of 

 the wall, the latter having decreased in thickness considerably opposite the 

 mesometrium. The blastocyst has arrived in the uterus. 



Fig. 3.— Utr. Mus. Cat. n°- Sorex 2 a, 5 r. 21 «. 



Fig. 4._ „ „ „ 52 e, 3 r. 26 s. 



