DEVELOPMENT OF THE FROG S EGG. 



299 



of the embryo on the affected side. The opposite side progressed 

 approximately at its normal, but comparatively greater, rate. As 

 a result, the flexure of the neural tube increased proportionate 

 to the developmental progress of the embryo. In other words, 

 as an embryo increased in age the angle formed by the trunk with 

 the tail became more and more acute until a condition was 

 arrived at finally in which the long axis of the trunk lay parallel 

 to that of the tail. 



The sketches presented with this paper are intended merely 

 to demonstrate the general morphological and histological fea- 

 tures which are characteristic of the development of these ab- 

 normal, U-shaped embryos. It may be stated, however, that 

 no great attempt has been made to make them faithfully repre- 

 sentative of all of the histological details of the tadpoles. In 

 many instances the drawings are composite. In every instance, 

 however, the basis of each drawing has been an actual specimen. 

 The figures are to be interpreted, therefore, as merely type 

 representatives of the numerous examples which are illustrative 

 of the peculiarities of this form of abnormal development. 



Fig. 2 represents an embryo in the early stages of development 



FIG. 2. 



viewed from the dorsal aspect. The deep furrow which pene- 

 trates from the left, to and beyond the center of the embryo 

 mass represents the line of apposition of the two portions of the 

 right flank of the embryo which is so bent upon itself that the 

 right surface of the tail region is in contact with the right surface 



