62 DYNAMICS OF HISTOGENESIS. II 



ovum (Conklin; Wilson). By the exclusion of this element in 

 sectioning experiments the subsequent, positional, en\dronmental 

 relation is as much destroyed as the absence of the myoplasm. It 

 may well be that the yellow pigmented zone is destined to assume a 

 certain subsequent 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 unwarranted and too broad. All the work tending to 

 support the generalization 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 the affirmative answer to this question 

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

 providing the exclusion of surrounding genn plasm has been accom- 

 plished so as to exclude totally tensional stresses of differential growth 

 of relational parts. 



The last statement is made due to the fact that W. H. Lewis came 

 to the conclusion that muscle self-differentiates from experiments 

 in which transplantation of tissues around the otic capsule of tad- 

 poles was 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 this piece re- 

 mained viable it was bound to reveal subsequently the same tissues 

 as in its normal location for the resultants of differential growth and 

 the potential, mechanical 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 posi- 

 tion. To ehcit the response of mesenchymal cells in the formation of 

 muscle tissue the proper optimum tensional stress stimulus must be 

 applied. In tissue differentiation, therefore, 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 quahty of stretching is important. The cormective 

 tissues are resultants of certain degrees of stresses. Muscular tissues, 

 on the other hand, are responses to still different types of stresses. 



