STUDIES IN THE DYNAMICS OF HISTOGENESIS. 



I. Tension of Duterential Growth as a Stimulus to Myogenesis. 



By EBEN J. CAREY. 



{From the Department of Anatomy, College of Medicine, Creighton University, 



Omaha) 



(Received for publication, January 17, 1920.) 



The prevalent opinion among embryologists in regard to the origin 

 of muscular tissue is that of self -differentiation. This is due largely 

 to the work of Wilson (1904) on Dentalium, and Conklin (1896-97, 

 1905) on Cynthia (Styela) partita and Crepidula in regard to the organ- 

 forming elements of the cytoplasm, and to the experimental work of 

 Harrison and Lewis (1904, 1905). Harrison ablated the spinal cord of 

 the tadpole prior to the growth of the peripheral nerves into the limb 

 buds. This operation eliminated any peculiar formation stimulus 

 emanating from the nervous system. Still the differentiation of the 

 contractile substance took place in the normal manner, as did the 

 grouping of fibers into the individual muscles. Lewis (1910) draws 

 the following conclusion based on Harrison's experiments, in regard 

 to the genesis of cross-striated muscle: 



"Thus it is seen that aU the constructive processes involved in the production 

 of the specific structure and arrangement of the muscle-fibres take place independ- 

 ently of stimuli from the nervous system and of the functional activity of the 

 muscles themselves. Cross-striated muscle tissue and the individual muscles are 

 thus self-differentiating." 



The fact that there is considerable muscular differentiation before 

 nerves estabhsh a connection with their corresponding muscles has 

 been shown byBardeen (1900, 1906-07), Harrison, and Carey (1918) in 

 the pig embryo. There is also considerable smooth muscle differentia- 

 tion in the descending colon of the pig before either the myenteric or 

 Auerbach's plexus is detected. 



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