TO THÉ EMBRYOLOGY OF AMPHIBIA. 17 



axis of the egg. In a similar manner, the position and size of 

 the blastopore in every stage is indicated by the vertical and 

 horizontal dotted lines, respectively vertical or parallel to the 

 standard line. I may also explain here that when a " side-view " 

 of an egg is mentioned, that view of the egg is meant which 

 has the middle point of the dorsal lip of the blastopore just on 

 the edge of the egg-outline. When this edge is on the right hand 

 of the figure, the view is the " left " view ; and if on the left 

 hand, it is the " right " view. The " posterior view " of an 

 egg is the one which has the middle point of the dorsal lip 

 of the blastopore on the middle line of the microscopic field. 

 When once the positions of these views are accurately deter- 

 mined on the graduated scale on the rim of the rotating dish, 

 they are very useful in orienting the egg and in finding these same 

 views again in the further course of development. I generally made 

 it my practice to prepare two sets of drawings at every stage. 

 The first set was drawn from what I judged by my eye to be 

 the side and posterior views of the egg without reference to the 

 graduated scales of the rotating dish. The second set was drawn 

 by turning the dish to points on the graduated scale which 

 ought to give these views as determined in the earliest observed 

 stage of the egg. When discrepancies appeared between these 

 two sets, I generally determined what ought to be considered 

 as the true side and posterior views, by a comparison of the 

 drawings and a careful study of the actual object. 



I had hoped to give the exact measurements of the changes 

 in the position and size of the gradually closing blastopore at 

 every stage. I found, however, that basing such measurements 

 on sketches or drawings which necessarily have to be made rapidly 

 in order to mark the conditions at any given moment, would lead 



