300 



PRINCIPLES OF EMBRYOLOGY 



Many other combinations between tissues from different species of 

 Amphibia have been made experimentally. They often exert influences 

 on one another's growth but these differences are not always mutual. 

 Rotmann (1933) for instance, found that if on the body of a newt of the 

 species Triton taeniatus a limb was provided with a core of mesoderm of the 



10 20 30 40 50 60 70 80 90 100 110 120 130 140 

 Days after operation 



Figure 13.10 



Relative growth of eye-cup and lens in inter-specific grafts in Amblystoma. 

 Curve A, growth of tigrinum lens whefi associated with tigrinum eye-cup; 

 curve B, growth of tigrinum lens when associated with punctatum eye-cup. 

 The size of the lens is expressed as the ratio tigrinum lens to punctatum lens 

 of same age. Note that the tigrinum lens in its own eye-cup reaches about 

 i'6o times the punctatum size, but when combined with a. punctatum eye-cup 

 only about 1-30 times. Curve C shows the growth o£ a. punctatum eye-cup 

 provided with a tigrinum lens, the 'size index' being its ratio to a normal 

 punctatum eye-cup. Note that it becomes larger than usual, to about the 

 extent required to fit the associated tigrinum lens. (After data of Harrison.) 



species T. cristatus, but enclosed in skin belonging to the host's species, 

 the form of the limb up to the time of metamorphosis was entirely dic- 

 tated by the species that contributed the mesoderm, which imposed its 

 own growth rate on the ectoderm without being in any way influenced 

 by it (Fig. 13. 11). Interesting also in this respect are the experiments of 

 Baltzer (see 1952^) who, however, was concerned not only with the 

 growth rate in organs compounded out of combinations of tissues from 

 two different species, but even more with the original induction of the 

 organs and the laying down of their basic structure. On the whole he 



