igS CLARKE. [Vol. V. 



tilian as yet about the head, excepting the eyes. The wall 

 of the body has not yet closed over the largely developed vis- 

 cera, and the double tube from the body to the yolk-sac is seen 

 in Fig. 43. This double tube, as seen in Fig. 47, proves to 

 be portions of the intestine. They are shown in position in 

 Fig. 46, which is of an embryo in the thirty-fifth day of incuba- 

 tion, measuring 53 mm. in length. This embryo, dissected, is 

 represented in Fig. 47. Here one can trace with greatest clear- 

 ness the intestine from the stomach outward to the yolk-sac ; 

 and in the same way the hind gut, starting from the rectum, 

 proceeds outward to the same point on the yolk-sac as shown in 

 Figs. 43 and 50. When the remnants of the yolk-sac are drawn 

 into the body, the projecting intestine goes with it. Fig. 44 is 

 of an older embryo than 43, and 45 and 46 are older stages than 

 44. The position of the head at right angles to the body still 

 persists ; it is not much longer than broad, and the mouth is 

 scarcely larger than that of a bird at the same stage. There 

 are, even at this late stage, only the special reptilian characters 

 of the elongated eye and the somewhat elongated mouth, and 

 the greater length of tail. 



Figs. 48 to 51 are a series of the same egg and embryo about 

 five weeks old. In Fig. 48 the egg-shell and membrane have 

 been cut away, and the white of one side has been cut out up 

 to the thickened edge, where it firmly adheres to the shell 

 membrane. The white in the other end of the egg is in place, 

 and also the thin pellicle of white which lies over the region of 

 the embryo. 



In Fig. 49 the shell and shell membrane, together with all the 

 white, are cut away, showing the embryo within the amnion, 

 lying on the yolk. The blood-vessels pass through the amnion 

 to the vascular area of the yolk, which is clearer than the larger 

 mottled non-vascular part. 



In Fig. 50 the amnion has been cut away, and the embryo 

 turned over to one side ; this displays the arrangement of the 

 blood-vessels, and also the two branches of the intestine, which 

 form a long loop reaching out to the surface of the yolk. In 

 Fig. 51 a longitudinal incision has been made in the yolk-sac, 

 showing that the wall in the vascular area is much thinner than 

 that in the non-vascular, and that the blood-vessels ramify for 

 some distance in the thick walls of the latter area. 



