182 "WARREN H. LEWIS AND MARGARET 7?. LEWIS 



duo to a r(Hlift'(>nMitiati()ii or are nMuiiaiits of the cross striations 

 of the old libor.s which have been carried out hito the muscle 

 bud. In regenerating luamniahan muscle fibers Waldeyer has 

 pictured isolated groups of cross striations in the young muscle 

 bud which were apparently cari'ied out into the muscle bud and 

 so do not indicate the beginning of redifferentiation. From 

 the work of Waldeyer, Volkman, Ziegler and others it is well 

 known that the regenerating muscle buds in mammals are in 

 the early stages entirely devoid of cross-striations except for 

 such instances as quoted above. 



The similarity between the muscle buds in tissue cultures 

 and those pictured for the regeneration of muscle in mammals 

 indicates that we have here in tissue cultures a process essen- 

 tially the same so far as the initial stages are concerned. 



The cytoplasm in the living cultures shows a very fine striation 

 which has in general a longitudinal direction. This gives to 

 the cytoplasm of the muscle bud a very characteristic appear- 

 ance that distinguishes the muscle buds and the isolated fibers 

 from other cells of the culture. One gets the impression that 

 this cytoplasm has a firmer consistency than that of the mesen- 

 chyme cells. The cytoplasm is also somewhat more refractive 

 than that of the mesenchyme. These longitudinal striae are 

 much finer than the so-called sarcostyles or myofibrils seen in 

 fixed normal muscle. The myofibrils are apparently wanting 

 in the muscle buds of the tissue cultures and in the early buds 

 of regenerating muscle. 



Cultures fixed in osmic acid show the same characteristic 

 fine longitudinal striations. This is evspecially well seen in the 

 expanded ends of the muscle buds (figs. 6, 11). 



In some of the fixed preparations it is not uncommon to find 

 in the muscle buds especially in the enlarged ends, spindle- 

 Fig. 9 Protoplasmic end of muscle bud from eleven day chick embrj'o cul- 

 tivated in 90 per cent Locke's solution plus 10 per cent bouillon plus 0.5 per 

 cent dextrose for two days. 



Figs. 10 and 11 Protoplasmic ends from muscle bud of the wing of an eight 

 day chick embryo cultivated in Locke's solution plus 0.5 per cent dextrose for 

 three days. Figure 11 shows the striae and spindles. 



