PLATE II 



EXPLANATION OF FIGURES 



30. One of the five somite embryos (III) of vesicle No. 18 (see figs. 14 and 32). 

 Note how tlie embryo is attached to the Trager by means of the belly-stalk (b.s.). 

 The area vasculosa, like that of the chick, does not extend in to the embryo, but 

 is separated from it by a clear space which corresponds to the area pellucida. On 

 the right is seen the compound sinus terminalis (s.L) lying between the vascular 

 areas of the two contiguous embryos. The posterior prolongation of the amnion 

 is not clearly seen, but its extreme tip is indicated by the leader, p. am. X 16. 



31. A seven somite embryo (I) of this same vesicle. For a description of this 

 embryo see the detailed drawing shown in fig. 15. X 16. 



32. The dorsal view of the vesicle reconstructed in detail in fig. 14. The cervix 

 end is slightly torn and is turned under, consequently the common amnion and its 

 canals are not shown in the photograph. The turning under of the torn piece also 

 makes the vesicle appear shorter than it really is. At o.m. may be seen the scale- 

 like villi beginning to overgrow the lower portion of the yolk-sac. X 2.15. 



33. A vesicle cut open along the mid-ventral line and spread apart to show the 

 pairing of the embryos. It will be noted that the embryos are arranged so that the 

 right-hand pair (III and IV) is the mirrored image of the left-hand pair (I and II). 

 At this stage the amnia are still distinct, and in shape are oval with the broad end 

 directed toward the fundus. X i 



