POLYEMBRYONIC DEVELOPMENT IN TATUSIA 



615 



the pair of canals united at a very short distance from the 

 vesicle, and thus entering it as a single short tube. Variations 

 from this are seen in those cases in which the union takes place 

 further and further away from the amniotic vesicle. In one of 

 the most extreme cases observed the two canals on one side 

 were united for a distance of about three millirneters from the 

 vesicle, or more than half way between the anterior end of the 

 embryo and the amniotic vesicle. 



Fig. 5 A free hand drawing of specimen No. 276, in which the embryonic 

 rudiments are well started. Each embryo is connected with the common amniotic 

 vesicle (C.A.V.} by means of a slender tube-like canal. In the living condition 

 the vesicle measured about 5 mm. high by 3 mm. at the widest point. X 11. 



The important point is that in all of these cases the paired 

 condition of the embryos is unmistakably clear, and I know of 

 no other way to account for this except to assume that it rests 

 upon the manner in which the pair of secondary buds arises 

 from the primary buds. If the secondary buds start soon after 

 the primary buds are formed, than a condition similar to that 

 seen in figure 5 might readily result; but if the primary bud has 

 made considerable progress in its extension from the vesicle 

 before the secondary buds arose from it, then we should expect 



