124 



S. R. DETWILER 



given in table 1 A. Four cases of the eleven positive experiments 

 yielded normal results. The limb bud, although originally two 

 segments anterior to the normal and in the region of the third 

 gill, gradually shifted caudally during differentiation and finally 

 assumed the orthotopic (normal) position. The third gill, 

 although late in making its appearance and at first very much 

 smaller than its counterpart, gradually developed to full size. 

 In this series of experiments no normal limbs developed in the 

 heterotopic position. Those which did permanentlj'^ occupy the 



TABLE 1 



A. Showing the effects of removing the gill ectoderm and mesoderm from the posterior 

 {third) gill swelling (fig. 2) and transplanting a limb into the excavated area, 

 B. Showing the results of removing the ectoderm and mesoderm from the entire 

 gill sioelling (fig. 3) and transplanting a limb into the denuded territory 



1 In all four cases the limb shifted caudally during development and finally 

 occupied the orthotopic position. 



The above table does not include one series of forty operations which were 

 made upon unsatisfactory material. The serial case numbers, however, have 

 been preserved (table 2). 



transplanted position developed into abnormal appendages, of 

 which 45 per cent were abortive. These limbs, in their initial 

 development, assumed the posture shown in figure 10, but, 

 curiously enough, they soon began to take on the typical posture 

 of the third gill, which failed to develop (fig. 6), and thej^ never 

 fully differentiated into free motile appendages. The first and 

 second gills in some cases developed quite normally, whereas in 

 others they were incomplete and abnormal in appearance. 



In case 15 (fig. 7) the limb, except for an imperfectly^ reduph- 

 cated hand, was normal and it functionated to a considerable 

 extent. The third gill was wanting, although the first and second 



