354 EBEN J. CAREY 



This highly differentiated tissue is now considered to self -develop, 

 for so-called muscle-forming elements have been identified in the 

 ovum. By the exclusion of this element in cutting experiments the 

 subsequent positional environmental relation is as much destroyed 

 as is the myoplasm. It may well be that the yellow pigmented 

 zone is destined subsequently to assume a certain relation in 

 development. This position may necessitate subjection to an 

 optimum tensional-stress stimulus due to the differential growth. 

 The conclusion of self-differentiation is consequently not entirely 

 warranted and is too broad. All the work tending to support the 

 generahzation that muscle self-differentiates excludes the inner, 

 environmental stimulus — the stretching or tensional stimulus of 

 differential growth. Has the isolated myoplasm been cultured and 

 found to form muscle? Only an affirmative answer to this question 

 will warrant the assertion that muscles self-develop, and then only 

 providing the exclusion of surrounding germ plasm has been accom- 

 plished so as to exclude totally tensional stresses of differential 

 growth of relational parts. 



The last statement is made since certain observers have con- 

 cluded that muscle self-differentiates in experiments in which 

 transplantation of tissues around the otic capsule of tadpoles were 

 performed. That musculature subsequently appears is not to be 

 wondered at, for the potencies or actualities of differential growth 

 were also misplaced with the transplant. If the piece remained 

 viable, it was certain to reveal subsequently the same tissue as in 

 its normal location, for the resultants of differential growth and the 

 potential mechnical stimulus due to space relation were left intact. 



Consequently, the potencies of a blastomere are as much a 

 function of its position as of its material substances. The material 

 substances receive and react to the stimulus. The stimulus is a 

 function of position. To elicit the response of mesenchymal cells 

 in the formation of muscle tissue the proper optimum tensional 

 stress stimulus must be apphed. In tissue differentiation, there- 

 fore, the stimulus as well as the reception and response must be 

 taken into consideration. 



Tensional stresses are of various kinds and degrees. The 

 quantity as well as the quality of stretching is important. The 



