CROSS STRIATED MUSCLE IN TISSUE CULTURES 179 



same genera^ direction as the muscle buds from which they 

 have p obabty separated. 



The muscle buds from the explanted pieces of the seven day 

 chick embryo are much slenderer than those shown in figure 4 

 from the leg of an eight day chick embryo. The latter culture 

 was made in Locke's solution plus a little yolk. Whether the 

 differences in the growth are the result of the difTerences in the 

 media is not clear. They do not seem to depend upon the 

 differences in the ages of the chicks fo:; we see in figure 3 the 

 slender type of growth from a nine day chick embryo, somewhat 

 similar to that from explants from the seven day chick embryo. 



It is not uncommon for branches to split off completely from 

 the outgrowing buds and to wander freely among the mesen- 

 chjaiie cells. 1^'uch isolated fibers may have one or two or sev- 

 eral nuclei. Some seem to come directly from the explanted 

 piece. The mononuclear and binuclear fibers are usually long 

 and slender, very pointed at both ends and resemble young 

 myoblasts. Others are somewhat irregular as in figure 13. 

 The multinuclear ones vary somewhat in shape but are UvSually 

 long and slender as in figure 12. Figures 2, 3, and 4 show vari- 

 ous types of these free fibers. Some of them represent the entire 

 peripheral end of a muscle bud and are more or less irregular, 

 occasionally branched. They all have a cytoplasmic texture 

 similar to that of the muscle buds and are easily distinguished 

 from the mesenchyme cells by this as well as by their charac- 

 teristic shape and by the nuclei. 



Occasionally the more proxhiial part of the muscle bud becomes 

 spread out into a thin veil-like membrane as in figure 14. Here 

 two neighboring fibers are thus spread out against the cover 

 slip and fused together to form an exceedingly thin membrane. 

 The general appearance of the entire culture was similar to that 

 shown in figure 4. The nuclei are abundant in this veil-like 

 membrane. 



Fig. 4 ^Muscle and mesenchyme outgrowth from an explanted piece of the 

 leg of an eight day chick embryo cultivated in Locke's solution plus 0.5 per 

 cent dextrose plus few drops of yolk for two days. The deeply staining muscle 

 buds and smaller isolated fibers are easily distinguisluMl from the mesenchyme. 

 Osmic acid vapor, iron hematoxylin. X 100. 



