12 MORGAN. [VOL. I. 



tail had reached the stage shown in Fig. 3, it was cut off as 

 indicated by the vertical line. There was left exposed at the 

 cut end the light-colored ectoderm of the major component and 

 the inner tissues of the minor component. The new tail that 

 developed had light ectoderm on the surface and a dark inte- 

 rior. Each part regenerated its specific tissue and was unin- 

 fluenced by the developing tissue of the other species. 



Two points present themselves for consideration. If the 

 tail of an ordinary tadpole be cut off and subsequently develop, 

 does the regenerated tail show the specific characters of the 

 normal tail or is it different ? I have examined the regener- 

 ated tails of both species and find that both the ectoderm and 

 the mesodermal pigment cells are like those of a normal tail. 

 It is, however, not very uncommon, both in regenerated tails 

 of normal tadpoles and also in grafted tadpoles, to find the 

 mesodermal pigment cells imperfectly developed, and in such 

 cases the specific character of the cells is riot obvious ; but 

 in all cases in which the pigment cells are well developed, the 

 specific character is readily seen, especially in the cells lying 

 along the central part of the tail. It should be stated, 

 however, that I have occasionally found isolated cells whose 

 character was doubtful, but the large majority of cells are 

 unquestionably like those of the tissue from which the new 

 tail arises. The second question is whether the ectoderm forms 

 new cells over the new part, or does the old ectoderm simply 

 extend out over the new part ? There is the appearance in the 

 regenerating tail of the formation of a new ectoderm at the tip 

 of the new tail, where the cells are more crowded together and 

 smaller than over the base of the tail. It is not improbable 

 that in addition to this new ectoderm the old ectoderm extends 

 also over a part of the new tail. 



Experiment III. - - In several cases the tail was cut off 

 obliquely, in much the same way as in Harrison's experiment. 

 Owing to the difference in pigmentation of the two kinds of 

 ectoderm, I could follow the subsequent history of each and 

 determine whether, along their line of contact, and in the region 

 where new cells are developing, the specific characters of the 

 cells are altered. 



