260 RICHAED ASSHETON. 



small darker segments. Preserved in chromic acid. Stain borax carmine. 

 Thickness of section '005 mm. x 420. 



Fig. 10 (Ovis 14, No. 2). — Age 6 days. Section through an embryo in 

 which the dark outer layer has become doubled at one pole. Preserved in 

 chomic acid. Stain hsemalum. Thickness of section '01 mm. X 380. 



Fig. 11 (Ovis 6, No. 1). — Age 7 days. Section of the segmenting ovum 

 of the sheep in which the doubling of the outer layer of dark cells is very 

 distinct, and the same layer has become thinner at the opposite pole. Pre- 

 served in chromic acid. Stain carmaluni. Thickness of section '0075 mm. 

 X 420. 



Pig. 12 (Ovis 4, No. 1). — Age 5| days. Section through an embryo of 

 the sheep in which the cavity of the blastocyst is beginning to be formed. 

 It aj)parently appears amongst the dark cells. Preserved in chromic acid. 

 Stain carmalum. Thickness of section "0075 mm. x 380. 



PLATE 16. 



Fig. 13 (Ovis 4, No. 1). — Another section through the same embryo as 

 fig. 12. X 380. 



Fig. 14 (Ovis 43, No. 1). — Age uncertain. Seclion through the embryo 

 of a sheep with cavity of the blastocyst well established. Preserved in 

 chromic acid. Stain carmalum. Thickness of section "0075 mm. x 380. 



Fig. 15 (Ovis 4, No. 2).— Age 5| days. Section through the embryo of a 

 sheep slightly more advanced than the above. Preserved in chromic acid. 

 Stain carmalum. X 380. 



Fig. 16 (Ovis 34, No. 1). — Age unknown. A section through the embryo 

 of a sheep just before the rupture of the zona radiata. Preserved in chromic 

 acid. Stain carmalum. Thickness of section -0075 mm. x 380. 



Fig. 17 (Ovis 34, No. 2). — Age unknown. A section through the embryo 

 of a sheep immediately after the rupture of the zona radiata. Thickness of 

 section -0075 mm. x 380. 



Fig. 18 (Ovis 42).— Age 9 days. 



Fig. 19. — Section through above along the line a — b. 



Fig. 20 (Ovis 8).— Age 10 days. 



Fig. 21.— Section through above specimen (Fig. 20) along the line a—b. 

 Preserved in chromic acid. Stain carmalum. Thickness of section -0075 mm. 

 X 380. 



Fig. 22.— Camera outline drawing of above section to show the extension 

 of the inner hypoblast layer. 



