CROSS STRIATED MUSCLE IN TISSUE CULTURES 181 



Some of the muscle buds seem to consist o" chains of myo- 

 blasts which extend far out into the culture. Such buds tend 

 to break up or give off the individual myoblasts. 



The muscle buds do not degenerate in the cultures as a rule 

 until after the mesenchyme cells. 



THE CYTOPLASM 



The muscle buds from the eight or nine day chick embryos 

 that arise from the cut ends of cross striated fibers are with very 

 rare exceptions entirely devoid of cross striations. Sections 

 through the explanted piece from a nine day chick embryo show 

 even after two or three days in vitro well marked cross striations 

 in most of the muscle fibers. The muscle fibers within the ex- 

 planted pieces then do not seem to suffer any loss of differ- 

 entiation. The area of transition between the cross striated 

 muscle fiber within the explant- and the unstriated muscle bud 

 covers a very short distance in which there is a gradual fading 

 out of the cross-striations. In one or two instances we have 

 seen in fixed specimens indications of cross-striations in the out- 

 growing muscle buds. Such cross-striations are not well marked 

 antl only occupy a small portion of the bud, usually at the edge 

 of the bud in the part of the liber connecting the protoplasmic 

 end with the old fiber in the explanted piece. These cross- 

 striations were not directly continuous with those in the old 

 fiber. Rarely also cross-striations are seen in the isolated myo- 

 blasts but in no cases were they well developed. We are not 

 prepared to state definitely whether such cross striations are 



Fig. 5 Muscle l)uds with many nuclei from an explanted piece of the leg of 

 an eight day chick embryo cultivated in Locke's solution plus bouillon plus 0.5 

 per cent dextrose plus 1 per cent distilled water for two days. Osmic acid 

 vapor, iron hematoxylin. X 100. 



P"ig. 6 Protoplasmic ending of muscle bud showing fine striae, spindles and 

 processes. Osmic acid vapor, iron hematoxylin. Leg eight day chick embryo, 

 cultivated in 80 per cent Locke's solution plus 20 per cent bouillon plus 0.5 per 

 cent dextrose for two days. X 525. 



Fig. 7 Another protoplasmic ending from the same specimen as the above. 



Fig. 8 From the same specimen as above showing fusion of two normal 

 buds. 



