214 



CLARKE. 



EXPLANATION OF PLATE XIII. 



(Figures 47, 48, 49, and 50 are by Mr. S. F. Denton; the others, except 45, are my own. Figure 45 

 is an outline of Figure 130, Balfour's " Comparative Embryology," drawn by Professor Haddon.) 



FlG. 43. The especial points in this figure are the large head, with the small lower 

 jaw, the shape of the limbs, the elongated tail, prominent allantois, and the double 

 attachment of the intestine to the yolk-sac. 



Fig. 44. The lower jaw is still small; the upper is slightly hooked, suggesting that 

 of a turtle, and the extremities of the limbs are changing. 



FlG. 45. Lacerta muralis, after Haddon. 



Fig. 46. An embryo about thirty-five days old. The lower jaw now equals the 

 upper in length; the ear is formed; the digits also; the body cavity is still widely 

 open, nearly from the pectoral to the pelvic girdle; the two portions of the intestine 

 to the yolk-sac are shown cut off; the head is yet at right angles to the body. 



FlG. 47. This is a dissection of the embryo shown in Fig. 46. It is to show the 

 arrangement of the intestine and its connection with the yolk-sac. The two parts of 

 the intestine have been turned to opposite sides for clearness. They lie side by side. 



Fig. 48. The shell and shell membrane have been removed from one side, dis- 

 playing the yolk, the embryo within the amnion, and the white at one end. At the 

 end, to the left, the white is untouched, and it also stretches as a thin pellicle across 

 the embryo. The heavy white ridges at either end of the embryo are the lines, along 

 which the white closely adheres to the shell membrane. Life size. 



FlG. 49. An embryo of the same age, removed from the shell. This shows more 

 clearly the amnion, the vascular, and the non-vascular areas of the yolk. This 

 embryo lies transversely, that of Fig. 48 longitudinally, in the egg. Life size. 



Fig. 50. The same embryo as in the last figure, with the amnion cut away; the 

 embryo turned to one side to show the vascular area of the yolk, and the two portions 

 of the intestine that are attached to the yolk-sac. Life size. 



Fig. 51. The same specimen, with a longitudinal incision through the thin-walled 

 vascular area. The remainder of the yolk has a much thicker wall. 



