560 A. A. W. HUBREOHT. 



.,he mesoblast stretching backwards. The future somatic mesoblast-cells 

 (also iu Figs. 57 — 60) are distinguished by their more flattened shape and 

 stronger absorption of staining reagents. 



Mus. Utr. Cat. n°- Sorex 75 b-, 1 r. 14, 15 s. 



Figs. 57 and 58. — Two sections through mesoblast that has originated 

 partly from the gastrula-ridge, partly from the annular zone of hypoblast ; 

 karyolytic figures determining the details of the latter process are very 

 distinct. 



Fig. 57.— Mus. Utr. Cat. n°- Sorex 73 ¥, 4 r. 21 s. 



Pig. 58.— „ „ „ 17 s. 



Figs. 59—61. — Three sections through other blastocysts in which further 

 confirmation of these karyolytic processes is distinct. 



In Fig. 59, .T indicates a spot where the dividing nuclei have just sepa- 

 rated and rearranged themselves. 



Fig. 59.— Mus. Utr. Cat. n°- Sorex 73 a\ 3 r. 28 s. 



Fig. 60.— „ „ „ 18 s. 



Fig. 61.— „ „ 73 c, 3 r. 13 s. 



(This latter section belongs to a series of which no surface reconstruction 

 is given.) 



PLATE XL. 



Figs. 63 — 64. — Three surface views (obtained by reconstruction from an 

 unbroken series of sections drawn with camera) of three embryos from the 

 same uterus (No. 45). The mesoblast, of which the outer boundary is indi- 

 cated by a dotted line, stretches some distance beyond the epiblastic shield. 

 It is in this stage already a continuous plate, only interrupted in the median 

 line below the epiblastic shield by the gastrula-ridge (_^?-.), the protochordal 

 wedge {pw.), and the protochordal plate (pp.). 



The arrows indicate the exact situations, and also the extent of the sections 

 figured under the corresponding numbers. 



Fig. 65. — The uterus. No. 45, natural size, drawn from the spirit specimen. 



Figs. 66 — 68. — Three sections through the embryonic region of Fig. 62. 

 pp. Protochordal plate, pw. Protochordal wedge, /i^, az. Remnants as yet 

 fairly distinct of the annular zone of modified hypoblast of Figs. 33 — 35. 

 Fig. 66.— Mus. Utr. Cat. n°- Sorex 45 c, 4 n 5 s. 

 Fig. 67.— „ „ „ 2 s. 



Fig. 68.— „ „ „ 3 r, 18 s. 



Fig. 69. — An oblique section through another embryonic shield of the 

 same stage. Letters as above. C. lludiment of a canal in tiic protochordal 

 wedge. 



Mus. Utr. Cat. n°- Sorex 45 e, 4 r. 10 s. 



