deposition, when the body of the embryo with several mesoblastic 

 somites and the rudiments of the Wolffian duct etc. are hardly raised 

 over the general surface of the egg. 

 Fig. 17. — Fish-like stage of an embryo on the 8th day after deposition. 



Sketched after being taken out of the vitelline membrane. 

 Fig. 18. — (a) Tadpole on the 10th day after deposition when it has just 

 hatched out but is still within the frothy substance. Number of 

 pigment spots beginning to appear at the thoracic region of the 

 tadpole over the upper surface of the spherical yolk mass, (b) 

 Blood-vessels in the external gills. 

 Fig. 19.— Tadpole on the 11th day after deposition. 



Figs. 20-38. Successive stages of the Rhacopliorus Egg C, 

 fixed on Zeiss's " Prismen Rotator " and observed with Zeiss's 

 Oc. I x Obj. a 2 . The horizontal basal lines under many of the 

 figures in this Plate indicate the surface of the mirror on which 

 the egg is resting. The lines drawn vertical to these show the 

 vertical axis of the rotating egg in successive stages. The hori- 

 zontal lines parallel to the basal lines through the central point 

 of these figures denote the equatorial plane of the rotating egg 

 in successive stages. The dotted and other lines in several 

 figures all denote the approximate position of the blastopore in 

 the successive stages of the rotating egg. 

 Fig. 20. — Side view of Egg C sketched at 2:30 p.m. of the first day after 



deposition. Stage intermediate between Figs. 7 and 8. 

 Fig. 21. — Posterior view of Egg C sketched at 2:25 p.m. of the second day 



after deposition and at the scale 217° of the mirror dish. 

 Fig. 22. — Upper view of Egg C showing the centrally situated large area 

 of the segmentation cavity, sketched at 2:30 p.m. of the second day. 

 Fig. 23. — Left side view of Egg C, sketched at 3:20 p.m. of the second day. 

 Fig. 24. — Lower view of Egg C, sketched at 7:00 a.m. of the third day 

 after deposition. The blastopore is diminishing by equal growth of 

 every part of its lip. 

 Fig. 25. — Upper view of Egg C, sketched about 5 minutes later than 

 Fig. 24. It shows that the diminution of the area of the segmenta- 

 tion cavity is also taking place centripetally. 

 Figs. 26, 27. — Left, and right, side views of Egg C just before its vertical 

 rotation begins. Sketched at 8:10 and 8:15 a.m. of the third day. 

 Fig. 28. — Left side view sketched at 9:43 a.m. of the third day when the 

 egg has- just begun to rotate, resting now on the ventral lip of the 

 gradually reducing blastopore. 

 Figs. 29, 30. — Lower, and upper, views of Egg C, sketched respectively at 

 9:57 and 10:00 a.m. of the third day. Both the areas of the 



