MORGAN. [VOL. I. 



It seemed possible, at least, that new tissue, composed of cells 

 derived from two species, might show the influence of its dual 



origin. 



Harrison 1 has shown that the tails of young tadpoles may 

 be interchanged even when two species are used, and that later 

 the ectoderm of the body of the larger component grows out 

 over the base of the grafted tail, slipping over the region where 

 the tail has been grafted on, as shown in Fig. i. If two 

 species be used, and then, after the tail has grown to the stage 

 shown in this figure, the tail be cut off just distal to the point 

 of union, as shown in Fig. 2 by the vertical line, there will be 

 present at the exposed end two kinds of tissue-- the ectoderm, 

 which is the same as that covering the body of the tadpole, and 

 the inner tissue, composed of muscles, connective tissue, pig- 



FIG. i. (After Harrison.) 



ment cells, notochord and nerve cord, that belong to the grafted 

 tail. Under these circumstances the new tail that regenerates 

 will be made up of parts of two species. Harrison carried 

 out an experiment of this sort. He writes 2 in regard to the 

 result : " The tail of a larva of R. virescens was replaced by the 

 tail of a larva of R. palustris, in the manner described above. 

 Forty-eight hours later, at which time the sketch was made 

 (see Fig. i), the tail was amputated. The epidermis from the 

 virescens body had then pushed out considerably over the root 

 of the tail, so that in cutting, almost all of the grafted epider- 

 mis (stippled in the figure) was removed. But a considerable 

 portion of the underlying organs of the transplanted piece 

 (shaded in the figure) remained, and it was from this compo- 

 nent that regeneration took place in all the tissues, with the 

 exception of part of the epidermis. The newly grown tail was 



1 Harrison, R. G., "The Growth and Regeneration of the Tail of the Frog 

 Larva," Roux's Archiv. Vol. vii, 1898. ~ Page 473. Case 13. 



