224 HUBERT DANA GOODALE 



hemisphere, depending upon the particular species. The posi- 

 tion of the head of the embryo seems correlated with the length 

 of the embryo, so that the longer the embryo, the higher up on 

 the egg it develops. It is interesting to note that the shorter 

 embryos of the frog and toad have a well-developed sense plate. 

 It may be w^e err in using the anterior connective as the basis 

 of our comparison of the lengths of the embryos. It would seem 

 as though the sense plate were as much a part of the embryo in 

 the narrower sense, as the neural folds themselves, even although 

 they do not function as sensory organs. 



Eggs marked about the equator 



When eggs are marked about the equator, a few hours before 

 gastrulation begins, with a series of spots, an interesting series 

 of movements of egg-material may be observed. The movement 

 described by Kopsch in the frog's egg are similar in some respects. 

 Bles ('05) has given a figure in which the pigment of a gastrulat- 

 ing egg of Xenopus laevis is arranged in bands similar to the ones 

 produced artificially in the eggs of Spelerpes. I have seen similar 

 natural streaks in the eggs of Amblj^stoma and one species of 

 frog. 



Records were kept by means of drawings on 34 eggs, 25 of which 

 were successful, although not all lived until the embryo appeared. 

 Confirmatory results have also appeared in eggs marked for other 

 purposes. 



The history of the marks as they appeared in the egg shown in 

 figs. 48-55 may be taken as a tj'pical case. It was one of a series 

 marked May 9, 8 p.m. The first drawing (fig. 48) was made next 

 morning at ten. The upper hemisphere only is shown since the 

 marks w^ere invisible from beneath. There are six stained spots 

 placed at unequal intervals about the egg, just above the equator. 

 For convenience of reference, the marks have been lettered. The 

 side of a mark nearest the blastopore is arbitrarily called the 

 proximal end, the other, the distal. At 3 p.m., the blastopore 

 had appeared, lying well below E and the equator, in the yolk- 

 cells and extending towards D. There was no change in the ap- 



