CROSS STRIATED MUSCLE IN TISSUE CULTURES 191 



tissues of early embryonic stages might continue to differentiate, 

 or remain stationary or dedifferentiate. In either case, patho- 

 logical changes and degeneration may supervene. We know 

 that the anlage of many tissues of amphibian embryos (central 

 nervous system, the eye, otic vesicle, notochord, voluntary 

 muscle, heart, etc.), when transplanted into strange environ- 

 ment of the same or another embryo will continue to differen- 

 tiate. There is a period during which many young embryonic 

 tissues are self-differentiating. It is not surprising then that 

 Harrison should have obtained an outgrowth of the axis cylin- 

 ders from young nerve cells and a differentiation of cross-striated 

 muscle from young embryonic myoblasts in tissue cultures. 

 On the other hand, it is perfectly evident that in older embrj^os 

 (chick embryos of nine days, for example) cross-striated muscle 

 as it grows out into the culture loses its cross-striations and as- 

 sumes a more embryonic condition. The portion of the fiber 

 which remains in the explanted piece retains, however, its cross- 

 striations. 



The muscle buds found in tissue cultures resemble in many 

 ways the early stages of the regeneration of muscle in the higher 

 mammals after injury or rupture of the muscle fibers as described 

 by Waldeyer ('63) and Volkmann ('83) and Ziegler ('98). In 

 mammals the buds which grow out from the cut ends of the 

 fibers are more or less homogeneous and unstriated. There are 

 often lateral buds as well. These buds elongate and extend be- 

 tween the connective tissue cells filling in the wound. Such 

 buds are crowded with nuclei which are supposed to increase 

 in number for the most part by direct division. Mitoses are 

 also found. There are also found free myoblasts, long spindle 

 cells with one or more nuclei, which come from the old piece. 

 There is also a disappearance of the cross-striations in the old 

 fibers near the cut ends. The process of regeneration is slow, 

 extending over weeks. A redifferentiation occurs in these buds 

 with the formation of longitudinal and cross-striations so that 

 finally they come to resemble the old fibers. The free myo- 

 blasts also differentiate in a manner similar to that of embryonic 

 myoblasts. 



