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enchymal cells have much less protoplasm than at the earlier stages. 

 The extreme distal end of the balancer is provided with a number 

 of thick sucker-like projections. Each of these processes is an out- 

 growth of a single ectodermal cell. By means of these the balancer 

 functions as a sucker. 



Regeneration, 



In a 3 mm embryo no trace of the balancer anläge is to be seen, 

 but by comparison with slightly older embryos one can determine 

 accurately the region from which the balancer will develop. The 

 ectoderm of the balancer-forming region with some of the underlying 

 mesoderm was removed from a number of 3 mm embryos. In nearly 

 every case the balancer was developed, though it appeared somewhat 

 later. It may attain to normal size but is usually smaller. 



The same operation was made on 4 mm embryos. A very small 

 short balancer was usually developed. 



Embryos immediately beyond this stage have a distinct balancer 

 anläge (cf. Fig. 1). If any part of the balancer be cut ofi from the 

 6 mm stage on, it is not regenerated. The entire balancer or distal 

 portions of it were removed from a number of older embryos. In no 

 case did any regeneration occur. The balancer then shows no power 

 of regeneration at any stage of development, at least not in the direc- 

 tion of its long axis. The tissue that is to form the organ may be 

 partly regenerated however if removed before any distinct elevation 

 is present. 



Transplantation. 



Exp. 82. The balancer ectoderm (i. e., the ectoderm in the posi- 

 tion from which the balancer develops) and a little of the underlying 

 mesoderm of a 3 mm embryo were transplanted on a denuded area 

 on the anterior end of the right side of another embryo of the same 

 length. The transplanted tissue developed into a balancer almost as 

 soon as the normal balancers appeared. It developed at about the 

 same rate and attained to about the same length as the normal organs 

 but was somewhat more slender (Fig. 8). It went through the retrogressive 

 changes and dropped off six days later than the normal balancers. In 

 two other successful transplantations in which some mesoderm was 

 included, the transplanted tissue developed into a balancer somewhat 

 smaller than normal. In each case the transplanted balancer dropped 

 off several days later than the normal. 



Several operations were made similar to the above except that 

 great care was taken to transplant only the ectoderm of the balancer- 

 forming region. In nearly every case a balancer developed from the 



